Add keyword "macos" to testlib blacklisting

With "macos" keyword in place, we can blacklist using that
keyword instead of the old "osx".

Change-Id: Ib7a2f88265271df152320cce8594b8f788b47687
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>
Reviewed-by: Jędrzej Nowacki <jedrzej.nowacki@qt.io>

src/testlib/qtestblacklist.cpp

@@ -104,6 +104,7 @@ static QSet<QByteArray> keywords()
 #endif
 #ifdef Q_OS_OSX
             << "osx"
+            << "macos"
 #endif
 #if defined(Q_OS_WIN) && !defined(Q_OS_WINRT)
             << "windows"