Baseline tests: wait longer before taking a screen snapshot

The recorded images frequently show traces of a fading-out command
prompt window that is opened by the test execution. We evidently have
to wait longer for all window-level effects are finished.

Pick-to: 6.5
Change-Id: I50db54ff33bf4bb1ef7c480a4aede1d5de1618c3
Reviewed-by: Santhosh Kumar <santhosh.kumar.selvaraj@qt.io>
Reviewed-by: Eirik Aavitsland <eirik.aavitsland@qt.io>

Author: vohi

tests/baseline/shared/qwidgetbaselinetest.cpp

@@ -124,8 +124,9 @@ QImage QWidgetBaselineTest::takeSnapshot()
 */
 QImage QWidgetBaselineTest::takeScreenSnapshot(const QRect& windowRect)
 {
-    // make sure all effects are done
-    QTest::qWait(250);
+    // make sure all effects are done - wait longer here because entire
+    // windows might be fading in and out.
+    QTest::qWait(750);
     return window->screen()->grabWindow(0, windowRect.x(), windowRect.y(),
                                         windowRect.width(), windowRect.height()).toImage();
 }