Fix variable not initialized warnings

```
activesupport/test/concern_test.rb:20: warning: instance variable
@included_ran not initialized

activesupport/test/concern_test.rb:28: warning: instance variable
@prepended_ran not initialized
```

activesupport/test/concern_test.rb

@@ -8,25 +8,11 @@ module Baz
     extend ActiveSupport::Concern
 
     class_methods do
+      attr_accessor :included_ran, :prepended_ran
+
       def baz
         "baz"
       end
-
-      def included_ran=(value)
-        @included_ran = value
-      end
-
-      def included_ran
-        @included_ran
-      end
-
-      def prepended_ran=(value)
-        @prepended_ran = value
-      end
-
-      def prepended_ran
-        @prepended_ran
-      end
     end
 
     included do