Enable confidential_epics by default on update

This was forgotten when the flag was enabled by default on other places.

ee/app/services/epics/update_service.rb

@@ -13,7 +13,7 @@ module Epics
       # start_date and end_date columns are no longer writable by users because those
       # are composite fields managed by the system.
       params.extract!(:start_date, :end_date)
-      params.extract!(:confidential) unless ::Feature.enabled?(:confidential_epics, group)
+      params.extract!(:confidential) unless ::Feature.enabled?(:confidential_epics, group, default_enabled: true)
 
       update_task_event(epic) || update(epic)