Fix insignificant QWidget test

qtbase/tests/auto/widgets/kernel/qwidget/qwidget.pro is marked as an insignificant_test, meaning that results are discarded and the test is not used by CI to block regressions. Futhermore, the test is currently disabled on mac and windows and is only being run on linux.

Examining recent CI logs shows that the test on linux reprots between 196 and 200 passes and between 27 and 29 fails. This means that about 200 test cases are potentially good and are being ignored.

Test coverage could be improved by using QEXPECT_FAIL to document the stable failures and QSKIP for the unstable failures. This would allow the insignificant_test marker to be removed so that the good part of the test can be used by CI to block regressions.