Tests: adding Pwhg Py8 UserHook as one of the possible Py8 control files
Similar to the modification in !3618 (merged),
in this merge request additionally just the inclusion of the bb4l Py8 UserHook PowhegBB4Ldlsl
suffices as one of the needed Powheg control files. This modification is needed to register bb4l Py8 showering job options, which shower the already existing Powheg bb4l LHE files and thus do not need the inclusion of e.g. the PowhegControl_bblvlv_Beta_modified_Common.py
control file.
Is this change fine, @sargyrop ?