Puts two regex layout tests back on the DumpRenderTree skipped list

fast/regex/test1.html and fast/regex/slow.html were removed from the skipped
list in https://android-git.corp.google.com/g/#change,43908

However, they cause DumpRenderTree to hang when run with V8, so are added back
to the list pending further investigation.

Bug: 2509394
Change-Id: I83c361c99fcd61e940a169f1ed00614529af48ff