Enforce running of job "form-generation" in CI

Change:
The idea of the MR is to make the CI-job form-generation run automatically again and don't allow it to fail. Currently it needs to be triggered manually and failure only generates a warning.

Reason:
While operator generation is what we aim for, some things are not supported, yet, e.g. DG elements. Also prototyping things in HyTeG is often simpler when one can work with a form and adapt an existing form-based operator to ones needs, instead of extending the operator generator and trying to answer the question whether the problem is with the generator or the FE side in HyTeG, when it fails.

Hence, in order to ensure that form generation remains working, I suggest to re-enable automatic testing for this functionality.