Fix tst_qthreadpool under high load.

The tasks might not have run yet at the time of the QCOMPARE, so we need
to acquire on the semaphore in order to ensure that this is the case,
just like in the previous testcase.

Change-Id: I1da72bb07c2f53760b3bf912fc26aaf10ed18d48
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>

tests/auto/corelib/thread/qthreadpool/tst_qthreadpool.cpp

@@ -381,6 +381,7 @@ void tst_QThreadPool::expiryTimeoutRace() // QTBUG-3786
         threadPool.start(&task);
         QThread::msleep(50); // exactly the same as the expiry timeout
     }
+    QVERIFY(task.semaphore.tryAcquire(numTasks, 10000));
     QCOMPARE(task.runCount.load(), numTasks);
     QVERIFY(threadPool.waitForDone(2000));
 }