CI needs to support Python 3.6

[Araneidae]

The standard Python on RHEL8 remains at version 3.6, so really this needs to be supported in CI!

[AlexanderWells-diamond]

I don't believe we can do this - the python3-pip-skeleton uses pyproject.toml for configuration, the current standard for recent versions of Python, and the support for that only arrives in setuptools versions from ~61. Unfortunately those versions of setuptools do not support Python 3.6 at all.

While it doesn't really help us, Python 3.6 is two years past EOL, and so I don't see much gain in trying to retrofit the builds to work with Python 3.6.

[Araneidae]

Well, at least we do have (slight half baked) support for newer versions of Python on RHEL8.