[PWGHF] Fix type of DstarToPiKPiBkg in data model (#10180)

Author: vkucera

PWGHF/DataModel/CandidateReconstructionTables.h

@@ -949,7 +949,7 @@ enum DecayType { DplusToPiKPi = 0,
                  XicToPKPi,
                  N3ProngDecays }; // always keep N3ProngDecays at the end
 
-static const int DstarToPiKPiBkg = DecayType::N3ProngDecays;
+static constexpr int DstarToPiKPiBkg = DecayType::N3ProngDecays;
 
 // Ds± → K± K∓ π± or D± → K± K∓ π±