autotests: Make testXdgShellClientRules more robust to CI being heavily loaded
FAIL! : TestXdgShellClientRules::testSizeApply() 'surfaceConfigureRequestedSpy->wait(10)' returned FALSE. () Loc: [/home/jenkins/workspace/Plasma/kwin/kf5-qt5 SUSEQt5.15/autotests/integration/xdgshellclient_rules_test.cpp(731)]
If CI is moderately loaded, 10ms may not be enough. I don't remember why 10ms timeout was added.