Properly configure coverage.py

[ChristophAlt]

• the coverage session was incorrectly configured to run on python 3.10
• codecov now shows failure if a PR decreases coverage and has less than 80% patch coverage
• coverage.py fails if the code coverage is below 60%

Additional remarks:

• I disabled macOS builds for now, because they take long and we'll focus on linux for now
• I opted to include tests in the coverage, because it is a helpful indicator to spot problems with the unittests

[ArneBinder]

This looks very cool!

But it looks like the coverage is still running over the tests, see the report in "combine coverage data and display human readable report" of the ci pipeline. We suddenly have a coverage of 60%, but I dont think we added any tests. Before it was 45%, see cov report here.