CI: Add python 3.11 to Github Actions tests

[terriko]

This is mostly a reminder for me to look at it after my meetings today, but if someone else wants to experiment with it first go ahead.

I think we should probably add python 3.11 to github actions so the tests are being run there regularly. We've been using pyupgrade to check for future compliance so I don't anticipate any problems EXCEPT that our CI is currently failing on a bunch of language scanner tests so those need to be fixed first.

[Molkree]

Adding 3.11 to the Linux matrix is trivial but what about Windows tests? Currently, Windows tests run on 3.10 but Windows long tests run on 3.9. Do we want to bump them by one version? So Win tests on 3.11 and long Win tests on 3.10? Or maybe the opposite with long tests on 3.11?

What about long/manyfail Linux tests? Should we keep them on 3.8?

[Molkree]

Related: what about adding a 3.11 classifier for PyPI in setup.py?

[terriko]

Yes, good thinking. We should definitely add a 3.11 tag for PyPI as soon as we're sure it actually works in 3.11