Don't user issuable_sort cookie for epics collection

changelogs/unreleased-ee/4114-epic-list-fix.yml

+---
+title: Don't user issuable_sort cookie for epics collection
+merge_request:
+author:
+type: fixed

ee/app/controllers/groups/epics_controller.rb

@@ -77,6 +77,10 @@ class Groups::EpicsController < Groups::ApplicationController
     @collection_type ||= 'Epic'
   end
 
+  # we don't support custom sorting for epics and therefore don't want to use the issuable_sort cookie
+  def set_sort_order_from_cookie
+  end
+
   def preload_for_collection
     @preload_for_collection ||= [:group, :author]
   end