[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 21085ab635)
(cherry picked from commit 3da29b02b3)
(cherry picked from commit 6169fba292)
(cherry picked from commit ab98900ea6)
(cherry picked from commit e406a63289)

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",
 		},