[PRIVACY] 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 https://github.com/go-gitea/gitea/pull/21655

(cherry picked from commit cd0b8b6852)
(cherry picked from commit 58d43867ca)
(cherry picked from commit f290b91e50)
(cherry picked from commit 5bd6d75554)
(cherry picked from commit e5d0abb592)
(cherry picked from commit 4b381ce77e)

services/cron/tasks_extended.go

@@ -146,7 +146,7 @@ func registerUpdateGiteaChecker() {
 	}
 	RegisterTaskFatal("update_checker", &UpdateCheckerConfig{
 		BaseConfig: BaseConfig{
-			Enabled:    true,
+			Enabled:    false,
 			RunAtStart: false,
 			Schedule:   "@every 168h",
 		},