Fix typo in GitANNSvc.cpp

Hlt/HltServices/src/GitANNSvc.cpp

@@ -207,7 +207,7 @@ class GitANNSvc : public ANNSvcBase {
       return {};
     }
     lumi_schema_t m;
-    m.size = sz;
+    m.size = sz->template get<unsigned>();
     std::transform( j->begin(), j->end(), std::back_inserter( m.counters ),
                     []( const nlohmann::json& k ) { return IIndexedLumiSchemaSvc::from_json( k ); } );
     return m;