Consider how to address the change of Python versions used in CI parts of the lesson

[bielsnohr]

Because Python is still quite a dynamic language, the released and stable versions are always changing. This means that the versions that should be used in the parts of the lesson about CI and build matrices are also always changing. The amount that needs to change isn't huge, but there is surrounding text that needs to get updated every time rather than just the numbers in the code snippets.

In conversation with @anenadic , we discussed some possible alternatives, one of which would be to point to https://devguide.python.org/versions/ and tell learners to pick 2 or 3 versions that are currently supported to put into their matrix. A supplementary feature would be to add Instructor notes around this once we are in the Workbench version of the course. Open to other ideas about how to handle this.