checkReason_ActiveWindow() started failing on Windows when run together with
other tests, but still passed on its own.
The offending tests was checkReason_focusWidget(), which showed a window but did
not wait for it to be active.
After adding this wait the whole test executable passes on Windows as well.
Amends fd87c8da82.
Change-Id: I384bc45176fcd7bf6f491a4f39b46464ba45693b
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>