Merge branch 'mct-error' into '21.0-mc16a'

Downgrade error message in MuonCreatorTool

See merge request !45131

Reconstruction/MuonIdentification/MuonCombinedBaseTools/src/MuonCreatorTool.cxx

 /*
-  Copyright (C) 2002-2017 CERN for the benefit of the ATLAS collaboration
+  Copyright (C) 2002-2021 CERN for the benefit of the ATLAS collaboration
 */
 
 /////////////////////////////////////////////////////////////////////////////
@@ -1369,7 +1369,7 @@ namespace MuonCombined {
       }
       */
     }else{
-      ATH_MSG_ERROR("No primary track particle set, deleting muon");
+      ATH_MSG_DEBUG("No primary track particle set, deleting muon");
       return false;
     }