MuonPRDTest: Fix clang warnings.

If a dtor is final, the class itself should also be final.

MuonSpectrometer/MuonValidation/MuonPRDTest/src/sTGCRDOVariables.h

 /*
-  Copyright (C) 2002-2020 CERN for the benefit of the ATLAS collaboration
+  Copyright (C) 2002-2021 CERN for the benefit of the ATLAS collaboration
 */
 
 #ifndef STGCRDOVARIABLES_H
@@ -10,7 +10,7 @@
 #include "AthenaBaseComps/AthMsgStreamMacros.h"
 #include <vector>
 
-class sTGCRDOVariables : public ValAlgVariables
+class sTGCRDOVariables final : public ValAlgVariables
 {
  public:
  sTGCRDOVariables(StoreGateSvc* evtStore,