Backport: fix the missing i18n key for update checker (go-gitea#18646)

Author: wxiaoguang

options/locale/locale_en-US.ini

@@ -2407,6 +2407,7 @@ dashboard.last_gc_pause = Last GC Pause
 dashboard.gc_times = GC Times
 dashboard.delete_old_actions = Delete all old actions from database
 dashboard.delete_old_actions.started = Delete all old actions from database started.
+dashboard.update_checker = Update checker
 
 users.user_manage_panel = User Account Management
 users.new_account = Create User Account