Update Github Actions

[JulienDoerner]

Dear all,

this PR adds two new actions.

1. The first one is to build the documentation and coverage report. It can be started manual by any CRPropa developer. The documentation and the report can be downloaded afterwards.
2. The second action is a test of the example notebooks. This test is based on the crpropa-testing test (Ubuntu 20, python3). The notebooks are converted to python scripts and executed afterwards. This test aims to check if interfaces are changed and whether the documentation is updated accordingly.
   At the moment this test excludes the notebooks: custom-photon-field, MHD_models, density_grid_sampling, lensing_cr and lensing_map. Those notebooks require external data, which are not provided within this repository.

Also in the notebooks the DINT/ELECA part is removed and some ploting is updated to newer matplotlib versions.

[lukasmerten]

requirements

[lukasmerten]

Hi @JulienDoerner
Looks in general good to me and is for sure a good approach to simplify the creation of the documentation and coverage report.
Also testing the notebooks is a good idea, from my pint of view. However, the ne new test is failing. Is that expected or went something wrong?

[JulienDoerner]

hey @lukasmerten,
The failing test is caused by the notebook secondaries/photons.ipynb. In my last execution of the test before the PR this test passed. I guess this is related to the problems described in #456. I guess we could deactivate this notebook until the reason for the failing test has been figured out.

[lukasmerten]

If re-running the test fixes the problem, which seems to be the case, we don't need to exclude the test. I will take a closer look at the doc and coverage action in the next days.

[lukasmerten]

From my point of view we can merge this, when the typo is fixed.

I'll approve it now, but let's wait another day or so for additional comments.