Updates for code base targeting Python 3.9

[abravalheri]

Includes automatic updates from Ruff

[henryiii]

Unrelated, these are the same until October. Might make more sense to just leave one of them, or use an intermediate value + 3.x.

[abravalheri]

Thanks @henryiii for the review, I will modify that.

[henryiii]

Don't know why the CI (Cirrus, I think) is stuck in queue.

[abravalheri]

Hi @henryiii, I have a question:

I noticed that you introduced this field in #229.

Is this necessary given that tool.mypy.version is set on pyproject.toml?

(The reason why I am asking is because I noticed it may prevent to run tox -e typecheck on development machines that don't have 3.9 installed).

[henryiii]

That's to keep the pip install installing libraries that still support this Python. It's more important if you keep support for EoL Pythons, or use scientific libraries that follow SPEC 0. This also happens with typeshed at some point after EoL.

If it works, feel free to remove, we can always re-add if it's a problem. I think we are closer to EoL now so it might be fine.

[abravalheri]

I see that makes sense and makes things more reliable...

Would we retain some of these gains if we replace base_python with setting PIP_PYTHON_VERSION=3.9 as environment variable inside tox.ini?

(I understand that this may not be fully reliable because some packages may be available for 3.9 but not work on 3.13 for example)

[abravalheri]

I see, apparently we cannot:

ERROR: Can not use any platform or abi specific options unless installing via '--target' or using '--dry-run'

So let's leave it like this for now.

Thanks @henryiii