GitHub Actions: Install multiple versions of Python in a single job

[cclauss]

https://github.com/actions/setup-python/releases/tag/v4.4.0

This should be much faster without all the repeated setup and teardown.

Run actions/setup-python@v4
Installed versions
  Successfully set up CPython (3.7.16)
  Successfully set up CPython (3.8.16)
  Successfully set up CPython (3.9.16)
  Successfully set up CPython (3.10.10)
  Successfully set up CPython (3.11.2)

The process of using tox -e ALL seems to work perfectly but the long build and test times are the deal breaker.
We end up with a single long-running process instead of multiple processes running in parallel.

Thanks for your contribution

Please, make sure you address all the checklists (for details on how, see
development documentation)!

• ran the linter to address style issues (tox -e fix)
• wrote descriptive pull request text
• ensured there are test(s) validating the fix
• added a news fragment in docs/changelog folder
• updated/extended the documentation