[Test refactor 4/5] Improve the scheduled tests
The scheduled tests now leverage a docker container pre-built two hours earlier than this run by the CI.

It generates a job for each folder in the `tests` folder.
_The documentation is not available anymore as the PR was closed or merged._<|||||>Very cool!<|||||>Looks good to me! Also great that all `generation` tests from `test_generation_utils.py` are run! The errors:

```
ImportError: cannot import name 'json' from 'itsdangerous' (/usr/local/lib/python3.8/dist-packages/itsdangerous/__init__.py)
```

will be fixed once the previous PRs are merged?<|||||>> Looks good to me! Also great that all `generation` tests from `test_generation_utils.py` are run! The errors:
> 
> ```
> ImportError: cannot import name 'json' from 'itsdangerous' (/usr/local/lib/python3.8/dist-packages/itsdangerous/__init__.py)
> ```
> 
> will be fixed once the previous PRs are merged?

Actually encountered this problem locally now as well -> think we need to pin the `itsdangerous` library: https://serverfault.com/questions/1094062/error-from-itsdangerous-import-json-as-json-importerror-cannot-import-name-j