Update legacy ATLFAST3F_G4MS configuration (ATLASSIM-6935)

Tweak for legacy ATLFAST3F_G4MS configuration in order to make the output agree with CA (ATLASSIM-6935)

Simulation/ISF/ISF_Core/ISF_Algorithms/python/collection_merger_helpers.py

@@ -33,7 +33,7 @@ def generate_mergeable_collection_name(bare_collection_name,
         merger_input_collections = getattr(collection_merger,
                                            input_attribute_name)
         merger_input_collections.append(mergeable_collection)
-        merger_input_collections.sort()
+        merger_input_collections.sort(reverse=ISF_Flags.Simulator.usesFatras()) # temporary workaround
     elif athenaCommonFlags.DoFullChain() and DetFlags.pileup.any_on():
         mergeable_collection = hardscatterSG+bare_collection_name
     else: