Add Python 3.x.0 to CI tests

[notatallshaw]

What's the problem this feature will solve?

We've seen several times that due to bug fixes, or other backports, that PRs will work on the latest Python 3.x.y but will break on 3.x.z where z < y.

Describe the solution you'd like

For one platform (probably Linux) we add tests for all major version of Python we support, e.g. 3.9.0, 3.10.0, 3.11.0, 3.12.0, 3.13.0, to try and catch these issues, on the assumption that the ".0" version is most likely to trigger these bug collisions.

Alternative Solutions

If this is thought to add too much time on to the CI run I propose we add the very oldest version, e.g. 3.9.0. As this will presumably have the least bug fixes and backports of any version.

Additional context

There is an open question I guess if pip "supports" old bugfix versions of Python, but it seems that upgrading pip is easier than upgrading Python. And there isn't a good way to tell users to upgrade Python before upgrading pip.

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