Touch contents updated_at column in pure SQL

Instead of touching each content on its own.

app/models/concerns/alchemy/content_touching.rb

@@ -17,7 +17,7 @@ def self.included(base)
     #
     def touch_contents
       return unless respond_to?(:contents)
-      contents.each(&:touch)
+      contents.update_all(updated_at: Time.current)
     end
   end
 end