Use the skip forgery protection helper in Active Storage guide

The helper method is essentially a wrapper around skipping the callback,
and it simplifies the doc example.

[ci skip]

Author: carlosantoniodasilva

guides/source/active_storage_overview.md

@@ -1293,7 +1293,7 @@ the Rails application, similar to the following:
 
 ```ruby
 class DirectUploadsController < ActiveStorage::DirectUploadsController
-  skip_before_action :verify_authenticity_token
+  skip_forgery_protection
   before_action :authenticate!
 
   def authenticate!