Update Python versions in CI and setup.py

[dplarson]

Related to issue #763:

We should review the Python versions in the CI pipelines and setup.py to make sure they 1) include all stable versions and 2) remove any "obsolete" / unsupported versions.

Currently we include Python 3.7, 3.8, and 3.9, but since this has last been reviewed, Python 3.10 and 3.11 have been released. The Python 3.7 release schedule (https://peps.python.org/pep-0537/) says 3.7 is in security updates until June 2023, while Python 3.8 is in security updates until October 2024 (https://peps.python.org/pep-0569/). That's not to say we should automatically remove Python 3.7 but rather that we should consider removing support of older versions of Python when we're also considering adding newer versions. (This may also become necessary due to some package dependencies, e.g., numpy 1.22 dropped Python 3.7 support.)

[dplarson]

The CI pipelines for PRs are defined in .github/wrkflows/main.yml