Enable python 3.12 rc on GitHub Actions

[adiroiban]

GHA has 3.12 alpha

I think that we can give it a try and prepare Twisted for the future Python version.

@hrnciar has already started some cleanup for deprecated and now removed functions.

I think that more will be removed ... crypto / spwd

List of modules here https://peps.python.org/pep-0594/#deprecated-modules

For 3.12 I think that we are ok, so I expect this to be easy.

3.13 will be more complicated with the removal of cgi and spwd

[graingert]

closing in favour of #11888