QTestEventLoop: don't stop the test fails outside the main thread

This amends commit 115f828ae4
"QTestEventLoop: stop when the test fails" from Qt 6.3 to not attempt to
stop the QTestEventLoop instance if the failure happened outside the
main thread. This is to prevent the QTEL from being created outside the
main thread and thus cause warnings about QObject in addition to and
logged before the real test failure.

[ChangeLog][QtTest][QTestEventLoop] The QTestEventLoop no longer
attempts to exit its event loop if the failure was detected outside the
main thread.

 QWARN  : tst_QMutex::tryLock_non_recursive() QObject: Cannot create children for a parent that is in a different thread.
 (Parent is QCoreApplication(0x7fffffffe710), parent's thread is QThread(0x802e29000), current thread is QThread(0x7fffffffd5a8)
 FAIL!  : tst_QMutex::tryLock_non_recursive() 'timer.elapsed() >= waitTime - systemTimersResolution' returned FALSE. ()

Change-Id: Ieab617d69f3b4b54ab30fffd175b139322a1f02c
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>

src/testlib/qtestresult.cpp

@@ -534,7 +534,8 @@ bool QTestResult::compare(bool success, const char *failureMsg,
 void QTestResult::addFailure(const char *message, const char *file, int line)
 {
     clearExpectFail();
-    QTestEventLoop::instance().exitLoop();
+    if (qApp && QThread::currentThread() == qApp->thread())
+        QTestEventLoop::instance().exitLoop();
 
     if (QTest::blacklistCurrentTest)
         QTestLog::addBFail(message, file, line);