Tests: add bb4l Beta Pwhg control file to list of PwhgPy8 needed control files

The new bb4l Powheg version uses a new control file, which is included into the list of Powheg+Pythia8 control files in this merge request. For example, in the NLO job options of ATLMCPROD-11627, the control file Pythia8_Powheg_Main31.py was wrongly included, which will be removed in the updated job options. To pass the tests, the new bb4l control file would need to be added. Otherwise, I can skip the tests in the pipeline. What would you prefer, @sargyrop ?