Disable update_checker cron tasks

- This is being disabled as it will weekly connect to a domain.
- This only affects existing installations, as new installations will
have a explicit value being written into app.ini due to go-gitea#21655

services/cron/tasks_extended.go

@@ -151,7 +151,7 @@ func registerUpdateGiteaChecker() {
 	}
 	RegisterTaskFatal("update_checker", &UpdateCheckerConfig{
 		BaseConfig: BaseConfig{
-			Enabled:    true,
+			Enabled:    false,
 			RunAtStart: false,
 			Schedule:   "@every 168h",
 		},