Add testing and linting of notebooks to CI

[cchwala]

Add pytest run to CI for notebooks using nbmake and also run ruff linting.

• [x] closes the TODO to do add notebooks tests (not yet a separate issuse)
• [x] Tests added and passed if fixing a bug or adding a new feature
• [x] All code checks from pre-commit passed
• [ ] Added an entry in the whats-new file if fixing a bug or adding a new feature

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (b98404b) 100.00% compared to head (4d900ae) 100.00%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #11 +/- ## ========================================= Coverage 100.00% 100.00% ========================================= Files 2 2 Lines 20 20 ========================================= Hits 20 20 ```

:umbrella: View full report in Codecov by Sentry.
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[cchwala]

CI now fails for Windows... 🙈

ERROR: file or directory not found: docs/notebooks/*ipynb

[cchwala]

I tried many things to successfully run to run notebook tests also for Windows (see last commits...), but I could not get it to work.

Some ideas I tried are from this stackoverflow answer and the comments there, plus some variations.

I now dropped the test of the notebook for Windows, since it is IMO enough to test the notebooks on Linux and MacOS (actually one OS would be enough I guess) because our actual code is tested also on Windows and it is enough to just assure that the notebooks work in general, checking that there is nothing wrong with a missing dataset etc...

[cchwala]

I now also added linting of notebooks via ruff, see last commit 🚀