Fixes for CollectionMerger configuration for Run3 ATLFASTIIF_G4MS
This set of changes allows jobs running FATRAS to finish successfully for Run3 geometries.
It may be possible to clean things up further for ATLFASTIIF_G4MS jobs, where we don't need to support simulation of the Muon system in FATRAS, but that will require larger changes.
Tagging: @lmijovic, @pagacova, @golling, @tcuhadar, @sjiggins