The test was reporting wrong app size values and then
expecting a wrong height after subtracting the system
bar heights. This was happening because an older API
was still being used, using newer APIs fixes that.
Fixes: QTBUG-131338
Pick-to: 6.5
Change-Id: I7306ce62d9c683f84069cc19086a6cd28abf5441
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>
(cherry picked from commit 50603fddc535179ee02379a8807fe5cb104e0aae)