change created on to updated_on for issue list service

app/services/api/v1/issues/list_service.rb

@@ -94,7 +94,7 @@ class Api::V1::Issues::ListService < ApplicationService
     else
       scope = issues.includes(:priority, :issue_status, :user, :show_assigners, :show_issue_tags, :version, :comment_journals)
       scope = if sort_by == 'issue_priorities.position'
-                scope.reorder("issue_priorities.position #{sort_direction}, issues.created_on DESC").distinct
+                scope.reorder("issue_priorities.position #{sort_direction}, issues.updated_on DESC").distinct
               else
                 scope.reorder("#{sort_by} #{sort_direction}").distinct
               end