Rename before_filter to before_action

before_filter is deprecated in Rails 5, we should rather
use before_action

ee/app/controllers/groups/omniauth_callbacks_controller.rb

 class Groups::OmniauthCallbacksController < OmniauthCallbacksController
   extend ::Gitlab::Utils::Override
 
-  skip_before_filter :verify_authenticity_token, only: [:failure, :group_saml]
+  skip_before_action :verify_authenticity_token, only: [:failure, :group_saml]
 
   def group_saml
     @unauthenticated_group = Group.find_by_full_path(params[:group_id])