[Mac] [WK2] Layout Test fast/regions/fixed-pos-elem-in-region.html is flaky on Debug builders
https://bugs.webkit.org/show_bug.cgi?id=114571

* platform/mac-wk2/TestExpectations:
The bots are also seeing image failures flakily, so add that expectation.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@148774 268f45cc-cd09-0410-ab3c-d52691b4dbfc