Bump flake8 from 3.8.4 to 5.0.4 in /.github/workflows (#5)

Bumps [flake8](https://github.com/pycqa/flake8) from 3.8.4 to 5.0.4.
<details>
<summary>Commits</summary>
<ul>
<li><a
href="https://github.com/PyCQA/flake8/commit/6027577d325b0dd8bf1e465ebd29b71b5f0d005b"><code>6027577</code></a>
Release 5.0.4</li>
<li><a
href="https://github.com/PyCQA/flake8/commit/213e006ce61b3c155445235b3f0d9453391f1f13"><code>213e006</code></a>
Merge pull request <a
href="https://github-redirect.dependabot.com/pycqa/flake8/issues/1653">#1653</a>
from asottile/lower-bound-importlib-metadata</li>
<li><a
href="https://github.com/PyCQA/flake8/commit/e94ee2b5f1801354b940cfe830b9160852915aec"><code>e94ee2b</code></a>
require sufficiently new importlib-metadata</li>
<li><a
href="https://github.com/PyCQA/flake8/commit/318a86a4a12d28cdfc41030ead547332d3461f45"><code>318a86a</code></a>
Merge pull request <a
href="https://github-redirect.dependabot.com/pycqa/flake8/issues/1646">#1646</a>
from televi/main</li>
<li><a
href="https://github.com/PyCQA/flake8/commit/7b8b374c9bc1a141ca7cf6670c8cee6708398490"><code>7b8b374</code></a>
Clarify entry point naming</li>
<li><a
href="https://github.com/PyCQA/flake8/commit/7160561028ee5db09ea58b8555db08c66ee092b3"><code>7160561</code></a>
Merge pull request <a
href="https://github-redirect.dependabot.com/pycqa/flake8/issues/1649">#1649</a>
from PyCQA/pre-commit-ci-update-config</li>
<li><a
href="https://github.com/PyCQA/flake8/commit/84d56a8c25106b5e0a41cdf63b5de261f8da5c99"><code>84d56a8</code></a>
[pre-commit.ci] pre-commit autoupdate</li>
<li><a
href="https://github.com/PyCQA/flake8/commit/ff6569b87db8ae28c41b548071454de620ad14d5"><code>ff6569b</code></a>
Release 5.0.3</li>
<li><a
href="https://github.com/PyCQA/flake8/commit/e76b59ae44f46f7958d13b28bd2d7d9bdc0f5962"><code>e76b59a</code></a>
Merge pull request <a
href="https://github-redirect.dependabot.com/pycqa/flake8/issues/1648">#1648</a>
from PyCQA/invalid-syntax-partial-parse</li>
<li><a
href="https://github.com/PyCQA/flake8/commit/25e8ff18b30b58f1dabc1d20546ebc20fd775560"><code>25e8ff1</code></a>
ignore config files that partially parse as flake8 configs</li>
<li>Additional commits viewable in <a
href="https://github.com/pycqa/flake8/compare/3.8.4...5.0.4">compare
view</a></li>
</ul>
</details>
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</details>

.github/workflows/constraints.txt

@@ -1,5 +1,5 @@
 pip==21.0
 pre-commit==2.9.3
 black==20.8b1
-flake8==3.8.4
+flake8==5.0.4
 reorder-python-imports==2.3.6