Fixed formatting

patch generated by https://gitlab.cern.ch/lhcb/Phys/-/jobs/17974981

Moved from Phys@1352655b

Event/PhysEvent/include/Event/ParticleCombination.h

@@ -58,7 +58,7 @@ struct ParticleCombination {
 
   /** @brief Number of children stroed in the combination
    */
-  int numChildren() const { return sizeof...(InputTypes);} 
+  int numChildren() const { return sizeof...( InputTypes ); }
   /** @brief Squared-magnitude of the four momentum sum of the children.
    */
   Combination::details::fp mom2() const {