When the tested widget has a focus proxy, then we should check if the
current focus widget is not the same as that focus proxy before setting
it to be the widget that gets focus. This ensures that when back-tabbing
from a widget like QDoubleSpinBox that it will not get stuck inside that
widget and will back-tab to the next correct one.
Fixes: QTBUG-81097
Change-Id: I3f689c7715da7f3ce8c3d2f616041528f5778a2f
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>