Run tests CI periodically

[RohitPrasadBhatt]

Same issue as coquma-sim.
ATM, our GitHub actions for tests run on a push or PR merge. I would like to run them periodically as well (say every 6 hours). This is good because then our tests will automatically run periodically and if something fails in the whole workflow (say Mannheim spooler gets frozen etc.) we will get an email. Of course the tests have to be written such that they emulate the whole workflow, but this is anyways done.

And the reference :
https://docs.github.com/en/actions/learn-github-actions/events-that-trigger-workflows#scheduled-events