Add basic CI tests for
AthGeneration. This adds ~1.5 min only as tests are very fast. For now no reference comparison is done, but we may want to try it at some point.
This adds PH+Py8, H7, MG+Py8 and Sherpa tests with 13.6 TeV (Run 3). To test the testing machinery this is also done for PH+Py8 for 13 TeV and 14 TeV (Run 2 and Run 4).