Adds missing dependency to ActionView::TestCase::Behavior

* The module is needed for the `determine_constant_from_test_name`
  method.
* Without it, the including class is required to also include
  `ActiveSupport::Testing::ConstantLookup` or a `NoMethodError` will be
  raised upon instantiation of that class.
* Issue introduced in c0a24555

actionpack/lib/action_view/test_case.rb

@@ -47,6 +47,8 @@ module Behavior
       include ActionView::RecordIdentifier
       include ActionView::RoutingUrlFor
 
+      include ActiveSupport::Testing::ConstantLookup
+
       delegate :lookup_context, :to => :controller
       attr_accessor :controller, :output_buffer, :rendered