CI: Add Python 3.12, drop 3.9

[oyamad]

No description provided.

[coveralls]

coverage: 93.029% (-0.01%) from 93.041%
when pulling a2cdb67 on ci312
into bea8295 on main.

[oyamad]

• For python -m ensurepip --upgrade, refer to https://stackoverflow.com/questions/77364550/attributeerror-module-pkgutil-has-no-attribute-impimporter-did-you-mean.
• But it did not work for windows-latest python-version 3.12, so excluded.
• The ModuleNotFoundError: No module named 'urllib3.packages.six.moves' error was fixed by requiring urllib3>=2.

[oyamad]

Let me merge this.