Fix compilation warnings reported in http://atlas-computing.web.cern.ch/atlas-computing/links/distDirectory/gitwww/MASTERWebArea/ardoc_web_areamaster64BC7AthenaOpt/ARDOC_Log_2021-05-06T2130/MuonSpectrometer_MuonReconstruction_MuonTrackMakers_MuonTrackMakerTools_MuonTrackFinderTools.html
C.C: @ssnyder, @christos