tst_QWindow: Use showNormal() to prevent maximize/fullscreen interference

We don't want platform behavior for whether or not maximized/fullscreen
windows can be resized to affect the test for resize event propagation.

Change-Id: I8c118733ca5d2553aacf24d0b8debeb1a4e27103
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@digia.com>
Reviewed-by: Gunnar Sletta <gunnar.sletta@digia.com>

tests/auto/gui/kernel/qwindow/tst_qwindow.cpp

@@ -177,7 +177,7 @@ void tst_QWindow::resizeEventAfterResize()
 
     Window window;
     window.setGeometry(geometry);
-    window.show();
+    window.showNormal();
 
     QTRY_COMPARE(window.received(QEvent::Resize), 1);