DEV: Remove logical OR assignment of constants (#29201)

Constants should always be only assigned once. The logical OR assignment
of a constant is a relic of the past before we used zeitwerk for
autoloading and had bugs where a file could be loaded twice resulting in
constant redefinition warnings.

app/controllers/groups_controller.rb

@@ -595,7 +595,7 @@ class GroupsController < ApplicationController
     end
   end
 
-  MAX_NOTIFIED_OWNERS ||= 20
+  MAX_NOTIFIED_OWNERS = 20
 
   def request_membership
     params.require(:reason)