FsrUtils: Fix cppcheck warnings.

FsrUtils: Fix cppcheck warnings.

Pass strings/containers by const reference, not by value.

PhysicsAnalysis/AnalysisCommon/FsrUtils/FsrUtils/FsrPhotonTool.h

 /*
-  Copyright (C) 2002-2022 CERN for the benefit of the ATLAS collaboration
+  Copyright (C) 2002-2023 CERN for the benefit of the ATLAS collaboration
 */
 
 #ifndef FSRUTILS_FsrPhotonTool_H
@@ -73,8 +73,8 @@ namespace FSR {
         /// @}
     private:
         /// Need for the FSR search
-        std::vector<FsrCandidate>* sortFsrCandidates( std::vector< std::pair <const xAOD::IParticle*, double> > FsrCandList,
-                                                      std::string option="ET");
+        std::vector<FsrCandidate>* sortFsrCandidates( const std::vector< std::pair <const xAOD::IParticle*, double> >& FsrCandList,
+                                                      const std::string& option="ET");
         bool isOverlap(const xAOD::Electron_v1* electron, std::vector< std::pair <const xAOD::IParticle*, double> > phfsr,
                        unsigned int nofPhFsr);
         double deltaR(float muonEta, float muonPhi, float phEta, float phPhi) const;

PhysicsAnalysis/AnalysisCommon/FsrUtils/Root/FsrPhotonTool.cxx

 /*
-  Copyright (C) 2002-2022 CERN for the benefit of the ATLAS collaboration
+  Copyright (C) 2002-2023 CERN for the benefit of the ATLAS collaboration
 */
 
 #include <utility>
@@ -369,7 +369,7 @@ namespace FSR {
     }  // end of getFsrPhotons
 
 
-    std::vector<FsrCandidate>* FsrPhotonTool::sortFsrCandidates(std::vector< std::pair <const xAOD::IParticle*, double> > FsrCandList, std::string option)
+    std::vector<FsrCandidate>* FsrPhotonTool::sortFsrCandidates(const std::vector< std::pair <const xAOD::IParticle*, double> >& FsrCandList, const std::string& option)
     {
    
         m_fsrPhotons.clear();