Add support for Python 3.12

[hugovk]

The Python 3.12 release candidate is out! 🚀

Call to action

We strongly encourage maintainers of third-party Python projects to prepare their projects for 3.12 compatibilities during this phase, and where necessary publish Python 3.12 wheels on PyPI to be ready for the final release of 3.12.0.

[hugovk]

(GitHub has removed EOL Python 2.7 from GitHub Actions, I recommend dropping it entirely.)

[droideck]

Looks good!
Feel free to create another PR with Python 2 removal, or I'll do it later next week.

[hugovk]

Here we go: #12! It's built on top of this one to avoid merge conflicts.