[autotests] Another change for SceneQPainterTest::testX11Window to make it pass CI

Still missing ideas, theory is that rendering on Xwayland is too slow and
we have an invalid buffer or that reparenting took to long.

autotests/integration/scene_qpainter_test.cpp

@@ -35,6 +35,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include <KWayland/Client/shell.h>
 #include <KWayland/Client/surface.h>
 #include <KWayland/Client/pointer.h>
+#include <KWayland/Server/buffer_interface.h>
 #include <KWayland/Server/surface_interface.h>
 
 #include <QPainter>
@@ -341,6 +342,7 @@ void SceneQPainterTest::testX11Window()
     }
     QVERIFY(client->surface());
     QTRY_VERIFY(client->surface()->buffer());
+    QTRY_COMPARE(client->surface()->buffer()->data().size(), client->geometry().size());
 
     // enough time for rendering the window
     QTest::qWait(100);