Set @body_classes to admin layout (#9081)

app/controllers/settings/notifications_controller.rb

@@ -4,6 +4,7 @@ class Settings::NotificationsController < ApplicationController
   layout 'admin'
 
   before_action :authenticate_user!
+  before_action :set_body_classes
 
   def show; end
 
@@ -29,4 +30,8 @@ class Settings::NotificationsController < ApplicationController
       interactions: %i(must_be_follower must_be_following must_be_following_dm)
     )
   end
+
+  def set_body_classes
+    @body_classes = 'admin'
+  end
 end