test: Skipping tst_qmdisubwindow::setFont() as it's unstable

This unstable test is preventing some good changes from being
merged. Further investigation needs to follow, so people can
refer to QTBUG-22544 for a real fix.

Change-Id: I038e5f340ccd2562d0e67428af595a2bcfc8c11d
Reviewed-by: Olivier Goffart <ogoffart@kde.org>

tests/auto/widgets/widgets/qmdisubwindow/tst_qmdisubwindow.cpp

@@ -1819,6 +1819,7 @@ void tst_QMdiSubWindow::closeOnDoubleClick()
 
 void tst_QMdiSubWindow::setFont()
 {
+    QSKIP("This test function is unstable in CI, please see QTBUG-22544");
     QMdiArea mdiArea;
     QMdiSubWindow *subWindow = mdiArea.addSubWindow(new QPushButton(QLatin1String("test")));
     subWindow->resize(300, 100);