Fix docs documenting invalid @every for OLDER_THAN cron settings (g…

…o-gitea#24695) (go-gitea#24698)

Backport go-gitea#24695 by @yardenshoham

Looks like a copy-paste leftover

- Fixes go-gitea#20868

Co-authored-by: Yarden Shoham <git@yardenshoham.com>
(cherry picked from commit aa984f2)

docs/content/doc/administration/config-cheat-sheet.en-us.md

@@ -1041,7 +1041,7 @@ Default templates for project boards:
 - `RUN_AT_START`: **false**: Run tasks at start up time (if ENABLED).
 - `NOTICE_ON_SUCCESS`: **false**: Set to true to switch on success notices.
 - `SCHEDULE`: **@every 168h**: Cron syntax to set how often to check.
-- `OLDER_THAN`: **@every 8760h**: any action older than this expression will be deleted from database, suggest using `8760h` (1 year) because that's the max length of heatmap.
+- `OLDER_THAN`: **8760h**: any action older than this expression will be deleted from database, suggest using `8760h` (1 year) because that's the max length of heatmap.
 
 #### Cron -  Check for new Gitea versions (`cron.update_checker`)
 
@@ -1058,7 +1058,7 @@ Default templates for project boards:
 - `RUN_AT_START`: **false**: Run tasks at start up time (if ENABLED).
 - `NO_SUCCESS_NOTICE`: **false**: Set to true to switch off success notices.
 - `SCHEDULE`: **@every 168h**: Cron syntax to set how often to check.
-- `OLDER_THAN`: **@every 8760h**: any system notice older than this expression will be deleted from database.
+- `OLDER_THAN`: **8760h**: any system notice older than this expression will be deleted from database.
 
 #### Cron -  Garbage collect LFS pointers in repositories (`cron.gc_lfs`)