Conditionally check if dune-common python package is installed

Closes #313

requested review from @samuel.burbulla

assigned to @santiago.ospina

mentioned in issue #313

Started full nightly test since that covers many different cases of internal/external venv and build-dir: https://gitlab.dune-project.org/infrastructure/dune-nightly-test/-/pipelines/52981

Something broke and I'm not sure why this change would cause this https://gitlab.dune-project.org/infrastructure/dune-nightly-test/-/jobs/414033

Thanks for checking. It definitely saved us quite some headaches!

For the time being I suggest to always run the nightly tests and/or the githb action whenever a change is made to the Python cmake setup. There are just too many to use the bindings (and getting dune-testtools/codegen up and running again has now added another one

Makes sense :)

• Nightly build: https://gitlab.dune-project.org/infrastructure/dune-nightly-test/-/pipelines/52984
• GitHub Actions: https://github.com/dune-project/dune-testpypi/actions/runs/2733110988

added 1 commit

• 84aa5312 - Use error 77 to skip failed tests in CI

Compare with previous version

mentioned in issue #314

merged

mentioned in commit 9c84e06b

mentioned in commit 461b07d2

mentioned in merge request !1163 (merged)