[Qt] Unreviewed gardening. Skip two compositing tests, because They hit assertion fail after 140999.
https://bugs.webkit.org/show_bug.cgi?id=108257.

* platform/qt/TestExpectations:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@141416 268f45cc-cd09-0410-ab3c-d52691b4dbfc