Fix cron.repo_health_check schedule example in config cheat sheet (#10324)

Fixes #10274.

Co-authored-by: Lunny Xiao <[email protected]>

Author: neingeist

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

@@ -518,7 +518,7 @@ NB: You must `REDIRECT_MACARON_LOG` and have `DISABLE_ROUTER_LOG` set to `false`
 
 ### Cron - Repository Health Check (`cron.repo_health_check`)
 
-- `SCHEDULE`: **every 24h**: Cron syntax for scheduling repository health check.
+- `SCHEDULE`: **@every 24h**: Cron syntax for scheduling repository health check.
 - `TIMEOUT`: **60s**: Time duration syntax for health check execution timeout.
 - `ARGS`: **\<empty\>**: Arguments for command `git fsck`, e.g. `--unreachable --tags`. See more on http://git-scm.com/docs/git-fsck