Update minimum Python version to 3.8

[paulromano]

Description

This PR updates our minimum Python version to 3.8 since 3.7 is already past EOL. For CI configurations, I've replaced 3.7 with a new configuration for 3.12 so that it is tested.

Checklist

• [x] I have performed a self-review of my own code
• [x] I have run clang-format (version 15) on any C++ source files (if applicable)
• [x] I have followed the style guidelines for Python source files (if applicable)
• [x] I have made corresponding changes to the documentation (if applicable)
• [x] I have added tests that prove my fix is effective or that my feature works (if applicable)

[paulromano]

Unrelated to the original changes in this PR, the pip install of mpi4py broke due to a new version of setuptools (see mpi4py/mpi4py#484). I put a workaround in this PR that hopefully gets us back to a green check mark :crossed_fingers:

[shimwell]

I think setuptools 69.4.0 and 69.3.0 have just been yanked from pypi https://pypi.org/project/setuptools/#history

[shimwell]

Looks good, feel free to merge.

If not I will merge tomorrow.