Bump min Python version for GHA (and fix spurious CI error)

[abravalheri]

Since e47994c we are having problems with 3.8.

This PR updates the versions to support the oldest and newest supported stable Python versions.

Summary of changes

Closes #4717

Pull Request Checklist

• Changes have tests
• News fragment added in newsfragments/.
  (See documentation for details)

/cc @Avasam for pyright GHA.

[abravalheri]

It turns up we have more errors happening in the CI, see jaraco/skeleton#152.

[Avasam]

@abravalheri Can you also bump pythonVersion in pyrightconfig.json and python_version in mypy.ini even if it's currently commented out ?

Given the usual mentality with coherent-oss / skeleton projects, I think those can even be completely removed and it would be up to the user to tell their editor which Python version to test with at different moments (and handle their venv appropriatly).
For example using VSCode:

(or in the linter plugin settings, which can be done per-workspace, and Jason made it clear we're not in the business of pre-configuring workspaces for specific editors)

Rather than applying a minimum across the entire project, hoping it'd catch more issues during development.

[abravalheri]

Regarding https://github.com/pypa/setuptools/actions/runs/11596788203/job/32288690596?pr=4716#step:9:133, I am tempted to let it xfail on macOS given that it regards a deprecated code path.

>       assert installed == {'aproj.egg-link'}
E       AssertionError: assert set() == {'aproj.egg-link'}
E         
E         Extra items in the right set:
E         'aproj.egg-link'
E         Use -v to get more diff

/Users/runner/work/setuptools/setuptools/setuptools/tests/test_easy_install.py:1467: AssertionError

(This approach was implemented in b9dd033)

[abravalheri]

@Avasam, I bumped the versions in the files you suggested. We can decide later to remove them.

For now I just want to make the CI pass, so that we can keep the PRs going, later we can refine it.

There should probably be a separated PR to remove stuff like if sys.version_info <= (3, 8).

[Avasam]

There should probably be a separated PR to remove stuff like if sys.version_info <= (3, 8).

Certainly. I just figured bumping the value in config sounded appropriate for this PR.