[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)
(cherry picked from commit b6a9b1390d)
(cherry picked from commit 3674362871)
(cherry picked from commit af0f606fc1)
(cherry picked from commit 49560da6fb)
(cherry picked from commit ca06e27c5b)
(cherry picked from commit 163df86df5)
(cherry picked from commit 0391c6ae42)
(cherry picked from commit f282f2d42f)
(cherry picked from commit 68d31cf247)
(cherry picked from commit cfd4a479e9)
(cherry picked from commit add969bdf6)

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",
 		},