Streamline CI

[f-hafner]

I think we can optimize the CI runs. For instance, I think it is not necessary to run CI on draft pull requests.

We can take some inspirations from other repos from our colleagues, for instance https://github.com/dianna-ai/dianna/blame/main/.github/workflows/build.yml.

Here are some other links

• https://docs.github.com/en/actions/using-workflows/workflow-syntax-for-github-actions#jobsjob_idstrategyfail-fast
• https://docs.github.com/en/actions/using-workflows/events-that-trigger-workflows#pull_request
• https://docs.github.com/en/actions/using-workflows/workflow-syntax-for-github-actions#onevent_nametypes

[f-hafner]

also, I find the tests run extremely slowly (one run takes ~10 min), I was expecting much shorter. Is this because of tox? can we make this faster?