Fix tests depending on sort stability
* test/rexml/xpath/test_text.rb (test_ancestors): Array#sort may
not be stable. [ruby-core:76088] [Bug #12509]
* test/rss/test_maker_{0.9,1.0,2.0}.rb (test_items): ditto.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@56412 b2dd03c8-39d4-4d8f-98ff-823fe69b080e