tst_QQuickPopup::popupWindowPositioning is flaky

The initial investigation shows the window geometry change events were not in sequence.

The popup is made to show at the position (50, 50) in the beginning, but adding some debug message shows that the window goes back and forth between (0, 0) and (50, 50). This further triggers unnecessary geometry change, making the signal spy validation for the position change in this test case fail.

83427: ********* Start testing of tst_QQuickPopup *********
FAIL!  : tst_QQuickPopup::Basic::popupWindowPositioning() Compared values are not the same
   Actual   (xSpy.count()): 3
   Expected (1)           : 1
   Loc: [/home/qt/work/qt/qtdeclarative/tests/auto/quickcontrols/qquickpopup/tst_qquickpopup.cpp(2437)]
Totals: 78 passed, 1 failed, 4 skipped, 30 blacklisted, 65463ms