Default to latest Python patch versions

[TheJulianJES]

Proposed change

Defaults to latest Python patch versions.

Additional information

This actually works now. The linked PR caused different jobs in the workflow to always have the latest Python patch version if not pinned to a specific patch version already, even if the latest patch version is not cached in the GitHub runner (which is what previously caused failures/venv cache key misses):

• Use check-latest for setup-python action #33

[TheJulianJES]

If we go with this, this is also something we want to adjust in other projects where we currently pin specific versions.

The upsides of this change would be that we no longer need to keep all patch versions in the individual projects updated.
If we keep them pinned and not updated, we continue to run old Python versions, which may no longer be in GitHub runner cache, increasing test run time by 10 to 20 seconds per job in the CI workflow.

See further explanation in #33.