tst_QHashSeed: reset the global seed in each iteration

QHashSeed is not a random number generator (though it uses one). It
returns the same value over and over again unless you reset it to a new,
random seed.

Fixes: QTBUG-98480
Change-Id: I89446ea06b5742efb194fffd16ba36601f08d794
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>

tests/auto/corelib/tools/qhashseed/tst_qhashseed.cpp

@@ -152,6 +152,8 @@ void tst_QHashSeed::quality()
             ++oneThird;
         if (seed == BadSeed)
             ++badSeeds;
+
+        QHashSeed::resetRandomGlobalSeed();
     }
 
     // report out