Only check changed_files in testdata/

[chadsr]

I ran into some issues regarding the changed_files check in test.yml whilst trying to use the act tool for local actions runs/tests.

This small tweak, using git diff and specifying only the testdata dir seems to fix the issue.

act output on master:

master  v3.0.0                                                                                                                                                                                                                                                                                                         10482  19:43 
╰─ act -W .github/workflows/test.yml
[Test/runner / black-format (github-check)    ] 🚀  Start image=ghcr.io/catthehacker/ubuntu:full-20.04
[Test/runner / black-format (github-check)    ]   🐳  docker pull image=ghcr.io/catthehacker/ubuntu:full-20.04 platform= username= forcePull=false
[Test/runner / black-format (github-check)    ]   🐳  docker create image=ghcr.io/catthehacker/ubuntu:full-20.04 platform= entrypoint=["/usr/bin/tail" "-f" "/dev/null"] cmd=[]
[Test/runner / black-format (github-check)    ]   🐳  docker run image=ghcr.io/catthehacker/ubuntu:full-20.04 platform= entrypoint=["/usr/bin/tail" "-f" "/dev/null"] cmd=[]
[Test/runner / black-format (github-check)    ]   🐳  docker exec cmd=[mkdir -m 0777 -p /var/run/act] user=root workdir=
[Test/runner / black-format (github-check)    ]   🐳  docker cp src=/home/marvin/git/github/chadsr/action-black/. dst=/home/marvin/git/github/chadsr/action-black
[Test/runner / black-format (github-check)    ]   🐳  docker exec cmd=[mkdir -p /home/marvin/git/github/chadsr/action-black] user= workdir=
[Test/runner / black-format (github-check)    ] ⭐  Run actions/checkout@v2
[Test/runner / black-format (github-check)    ]   ✅  Success - actions/checkout@v2
[Test/runner / black-format (github-check)    ] ⭐  Run ./
[Test/runner / black-format (github-check)    ]   🐳  docker exec cmd=[bash --noprofile --norc -e -o pipefail /home/marvin/git/github/chadsr/action-black/workflow/composite-0.sh] user= workdir=
| [action-black] Installing reviewdog...
| reviewdog/reviewdog info checking GitHub for tag 'v0.13.0'
| reviewdog/reviewdog info found version: 0.13.0 for v0.13.0/Linux/x86_64
| reviewdog/reviewdog info installed /tmp/reviewdog
| [action-black] Installing black package...
| Collecting black
|   Downloading black-21.12b0-py3-none-any.whl (156 kB)
     |████████████████████████████████| 156 kB 3.9 MB/s
| Collecting tomli<2.0.0,>=0.2.6
|   Downloading tomli-1.2.2-py3-none-any.whl (12 kB)
| Collecting pathspec<1,>=0.9.0
|   Downloading pathspec-0.9.0-py2.py3-none-any.whl (31 kB)
| Collecting platformdirs>=2
|   Downloading platformdirs-2.4.0-py3-none-any.whl (14 kB)
| Requirement already satisfied, skipping upgrade: click>=7.1.2 in /usr/local/lib/python3.8/dist-packages (from black) (8.0.1)
| Collecting typing-extensions>=3.10.0.0
|   Downloading typing_extensions-4.0.1-py3-none-any.whl (22 kB)
| Collecting mypy-extensions>=0.4.3
|   Downloading mypy_extensions-0.4.3-py2.py3-none-any.whl (4.5 kB)
| Installing collected packages: tomli, pathspec, platformdirs, typing-extensions, mypy-extensions, black
| Successfully installed black-21.12b0 mypy-extensions-0.4.3 pathspec-0.9.0 platformdirs-2.4.0 tomli-1.2.2 typing-extensions-4.0.1
| [action-black] Checking python code with the black formatter and reviewdog...
| reviewdog: environment variable $REVIEWDOG_GITHUB_API_TOKEN is not set
| [action-black] Clean up reviewdog...
[Test/runner / black-format (github-check)    ]   ✅  Success - ./
[Test/runner / black-format (github-check)    ] ⭐  Run Check if code is left untouched (not formatted)
[Test/runner / black-format (github-check)    ]   🐳  docker exec cmd=[bash --noprofile --norc -e -o pipefail /home/marvin/git/github/chadsr/action-black/workflow/2] user= workdir=
| Changes detected!
[Test/runner / black-format (github-check)    ]   ❌  Failure - Check if code is left untouched (not formatted)
Error: exit with `FAILURE`: 1

act output on this branch:

fix/test-changes                                                                                                                                                                                                                                                                                                        10484  19:47 
╰─ act -W .github/workflows/test.yml
[Test/runner / black-format (github-check)    ] 🚀  Start image=ghcr.io/catthehacker/ubuntu:full-20.04
[Test/runner / black-format (github-check)    ]   🐳  docker pull image=ghcr.io/catthehacker/ubuntu:full-20.04 platform= username= forcePull=false
[Test/runner / black-format (github-check)    ]   🐳  docker create image=ghcr.io/catthehacker/ubuntu:full-20.04 platform= entrypoint=["/usr/bin/tail" "-f" "/dev/null"] cmd=[]
[Test/runner / black-format (github-check)    ]   🐳  docker run image=ghcr.io/catthehacker/ubuntu:full-20.04 platform= entrypoint=["/usr/bin/tail" "-f" "/dev/null"] cmd=[]
[Test/runner / black-format (github-check)    ]   🐳  docker exec cmd=[mkdir -m 0777 -p /var/run/act] user=root workdir=
[Test/runner / black-format (github-check)    ]   🐳  docker cp src=/home/marvin/git/github/chadsr/action-black/. dst=/home/marvin/git/github/chadsr/action-black
[Test/runner / black-format (github-check)    ]   🐳  docker exec cmd=[mkdir -p /home/marvin/git/github/chadsr/action-black] user= workdir=
[Test/runner / black-format (github-check)    ] ⭐  Run actions/checkout@v2
[Test/runner / black-format (github-check)    ]   ✅  Success - actions/checkout@v2
[Test/runner / black-format (github-check)    ] ⭐  Run ./
[Test/runner / black-format (github-check)    ]   🐳  docker exec cmd=[bash --noprofile --norc -e -o pipefail /home/marvin/git/github/chadsr/action-black/workflow/composite-0.sh] user= workdir=
| [action-black] Installing reviewdog...
| reviewdog/reviewdog info checking GitHub for tag 'v0.13.0'
| reviewdog/reviewdog info found version: 0.13.0 for v0.13.0/Linux/x86_64
| reviewdog/reviewdog info installed /tmp/reviewdog
| [action-black] Installing black package...
| Collecting black
|   Downloading black-21.12b0-py3-none-any.whl (156 kB)
     |████████████████████████████████| 156 kB 4.0 MB/s
| Collecting platformdirs>=2
|   Downloading platformdirs-2.4.0-py3-none-any.whl (14 kB)
| Collecting tomli<2.0.0,>=0.2.6
|   Downloading tomli-1.2.2-py3-none-any.whl (12 kB)
| Requirement already satisfied, skipping upgrade: click>=7.1.2 in /usr/local/lib/python3.8/dist-packages (from black) (8.0.1)
| Collecting pathspec<1,>=0.9.0
|   Downloading pathspec-0.9.0-py2.py3-none-any.whl (31 kB)
| Collecting mypy-extensions>=0.4.3
|   Downloading mypy_extensions-0.4.3-py2.py3-none-any.whl (4.5 kB)
| Collecting typing-extensions>=3.10.0.0
|   Downloading typing_extensions-4.0.1-py3-none-any.whl (22 kB)
| Installing collected packages: platformdirs, tomli, pathspec, mypy-extensions, typing-extensions, black
| Successfully installed black-21.12b0 mypy-extensions-0.4.3 pathspec-0.9.0 platformdirs-2.4.0 tomli-1.2.2 typing-extensions-4.0.1
| [action-black] Checking python code with the black formatter and reviewdog...
| reviewdog: environment variable $REVIEWDOG_GITHUB_API_TOKEN is not set
| [action-black] Clean up reviewdog...
[Test/runner / black-format (github-check)    ]   ✅  Success - ./
[Test/runner / black-format (github-check)    ] ⭐  Run Check if code is left untouched (not formatted)
[Test/runner / black-format (github-check)    ]   🐳  docker exec cmd=[bash --noprofile --norc -e -o pipefail /home/marvin/git/github/chadsr/action-black/workflow/2] user= workdir=
| No changes detected!
[Test/runner / black-format (github-check)    ]   ✅  Success - Check if code is left untouched (not formatted)

[rickstaa]

@chadsr First of all, thanks a lot for your pull request! Your pull request makes sense since we don't stage files in the tests. I will merge this into v3.0.1 so that you can perform local tests for #44 using act.

[review-dog]

Hi, @chadsr! We merged your PR to reviewdog! 🐶
Thank you for your contribution! ✨

We just invited you to join the @reviewdog organization on GitHub.
Accept the invite by visiting https://github.com/orgs/reviewdog/invitation.
By joining the team, you'll be a part of reviewdog community and can help the maintenance of reviewdog.

Thanks again!

[github-actions]

🚀 [bumpr] Bumped! New version:v3.0.1 Changes:v3.0.0...v3.0.1