Explicitly support Python 3.12

[FantasqueX]

What is the problem that this PR addresses?

• Explicitly support Python 3.12 in pyproject.toml.
• Use Python 3.12 in github actions
• add Python 3.12 to test matrix.
• add Python 3.12 to black target.

How did you solve it?

...

Checklist

• [x] I have read the Contributor's Guide.
• [x] I will check that all automated PR checks pass before the PR gets reviewed.