tst_QPromise: don't wait() indefinitely

In unit-tests, blocking operations should be timed, whenever possible,
so that a proper failure is logged instead of a watchdog timeout
(which is reported as a crash).

Wait for 60s and wrap the wait() in QVERIFY(). Since this can fail,
mark ThreadWrapper's dtor as non-noexcept.

Amends 385f0732d9.

Pick-to: 6.5 6.2
Change-Id: I3462017cb1a7580c901b98e9b1c3741853f32dc6
Reviewed-by: Ivan Solovev <ivan.solovev@qt.io>
(cherry picked from commit 32d12c2ebace41361c789e5aa58430ebf9f687b1)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

tests/auto/corelib/thread/qpromise/tst_qpromise.cpp

@@ -97,10 +97,10 @@ struct ThreadWrapper
     {
         t->start();
     }
-    void join() { t->wait(); }
-    ~ThreadWrapper()
+    void join() { QVERIFY(t->wait(60s)); }
+    ~ThreadWrapper() noexcept(false)
     {
-        t->wait();
+        join();
     }
 };
 #endif