Skip the full file check if the rntuple file has not been produced

[tmadlener]

BEGINRELEASENOTES

• Skip the check for the full file in case the RNTuple has not been produce (e.g. if podio hasn't been built with RNTuple support)

ENDRELEASENOTES

This is a slightly hackish solution that leverages pytests capabilities to skip tests rather than failing them. Unfortunately it returns a non-zero exit code in that case, so we need the SKIP_REGULAR_EXPRESSION (which we can now make a bit more narrow). This works around the same issue as AIDASoft/podio#677 but entirely within EDM4hep.

I tried first with cmake features, but neither REQUIRED_FILES nor FIXTURES_REQUIRED can be made to work at the moment, as both of them mark the test suite as failed if they are used to not run a test. See these discussions: first second