correct the ActionCacheTest from [7346]

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@7348 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

actionpack/test/controller/caching_test.rb

@@ -281,6 +281,8 @@ def test_xml_version_of_resource_is_treated_as_different_cache
   end
   
   def test_correct_content_type_is_returned_for_cache_hit
+    # run it twice to cache it the first time
+    get :index, :id => 'content-type.xml'
     get :index, :id => 'content-type.xml'
     assert_equal 'application/xml', @response.content_type
   end