added include <unordered_set> to fix Megalinter

Author: alcaliva

DPG/Tasks/AOTTrack/unitTestForReconstruction.cxx

@@ -31,6 +31,7 @@
 #include <memory>
 #include <random>
 #include <string>
+#include <unordered_set>
 #include <vector>
 
 using namespace o2::soa;