Fix QCOMPARE with enum classes.

As these are strongly typed, they won't implicitly convert to int, so make sure
to cast explicitly.

(cherry picked from commit 9626baae

, auto test
is not included)
Task-number: QTBUG-49597
Change-Id: I29c4331a9b0c61f2e60c2bcab5a99f65daa7060f
Reviewed-by: Olivier Goffart (Woboq GmbH) <ogoffart@woboq.com>

src/testlib/qtestcase.h

@@ -238,7 +238,7 @@ namespace QTest
     inline typename QtPrivate::QEnableIf<QtPrivate::IsQEnumHelper<T>::Value, char*>::Type toString(T e)
     {
         QMetaEnum me = QMetaEnum::fromType<T>();
-        return qstrdup(me.key(e));
+        return qstrdup(me.key(int(e))); // int cast is necessary to support enum classes
     }
 
     template <typename T> // Fallback