Update AC::Metal documentation example [ci skip]

Include proper module since AV was extracted form AP as mentioned in #14659.

actionpack/lib/action_controller/metal.rb

@@ -70,7 +70,8 @@ def build(action, app=nil, &block)
   # can do the following:
   #
   #   class HelloController < ActionController::Metal
-  #     include ActionController::Rendering
+  #     include AbstractController::Rendering
+  #     include ActionView::Layouts
   #     append_view_path "#{Rails.root}/app/views"
   #
   #     def index