tst_qwidget_window::tst_resize_count() is flaky on OpenSUSE and Ubuntu

According to Grafana tst_qwidget_window::tst_resize_count() is one of the flakiest tests currently.

https://testresults.qt.io/grafana/dashboard/db/coin-single-test-details?orgId=1&var-project=qt%2Fqtbase&var-testcase=tests%2Fauto%2Fgui%2Fkernel%2Fqguiapplication&var-testfunction=modalWindow&var-branch=5.10&var-branch=5.11&var-branch=5.9&var-branch=dev&var-inter=24h&from=now-14d&to=now

It's flaky on OpenSUSE and Ubuntu, but seemingly not other platforms. There also doesn't seem to be failures in 5.9 branch, so this seems to be caused by something in 5.10 branch and newer. The test itself didn't seem to have any relevant changes between branches. I was also unable to reproduce the failure manually.