Run the CI tests with both the earliest supported Python version and
the latest stable release.
The intent is to quickly notice when new features require adjusting
the oldest supported Python version and also detect when the latest
stable version breaks old code (as when 3.12 removed `imp` and we
witched to `importlib` in #311).
Based on the latest walk-through: https://github.com/github/codeql-action.
Gets rid of the warning:
Warning: 1 issue was detected with this workflow: git checkout HEAD^2 is no longer necessary. Please remove this step as Code Scanning recommends analyzing the merge commit for best results.
Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
