test run on 'push' confusing

[OnnoEbbens]

In the CI file there is a test that is run for a "push" event.

- name: Run notebooks
  if: ${{ github.event_name == 'push' }}
  run: |
    py.test ./tests -m "not notebooks"

The test is confusing because the test is named 'Run notebooks' while the only thing it doesn't run is the notebooks :)

Originally we wanted to test the notebooks only on a 'push' event. Nowadays we use readthedocs to test the notebooks. I think we can remove the tests on "push" completely since we require a PR to change anything to 'dev' or 'main'. Do you agree?