Improve document for ARTIFACT_RETENTION_DAYS (go-gitea#28646)

Follow go-gitea#28626

Author: wxiaoguang

custom/conf/app.example.ini

@@ -2571,7 +2571,7 @@ LEVEL = Info
 ;;
 ;; Default platform to get action plugins, `github` for `https://github.com`, `self` for the current Gitea instance.
 ;DEFAULT_ACTIONS_URL = github
-;; Default artifact retention time in days, default is 90 days
+;; Default artifact retention time in days. Artifacts could have their own retention periods by setting the `retention-days` option in `actions/upload-artifact` step.
 ;ARTIFACT_RETENTION_DAYS = 90
 ;; Timeout to stop the task which have running status, but haven't been updated for a long time
 ;ZOMBIE_TASK_TIMEOUT = 10m

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

@@ -1391,7 +1391,7 @@ PROXY_HOSTS = *.github.com
 - `DEFAULT_ACTIONS_URL`: **github**: Default platform to get action plugins, `github` for `https://github.com`, `self` for the current Gitea instance.
 - `STORAGE_TYPE`: **local**: Storage type for actions logs, `local` for local disk or `minio` for s3 compatible object storage service, default is `local` or other name defined with `[storage.xxx]`
 - `MINIO_BASE_PATH`: **actions_log/**: Minio base path on the bucket only available when STORAGE_TYPE is `minio`
-- `ARTIFACT_RETENTION_DAYS`: **90**: Default number of days to keep artifacts. This can be overridden in `actions/upload_artifact`. Set to 0 to disable artifact retention. Default is 90 days if not set. Each artifact can have it's own number of retention days.
+- `ARTIFACT_RETENTION_DAYS`: **90**: Default number of days to keep artifacts. Artifacts could have their own retention periods by setting the `retention-days` option in `actions/upload-artifact` step.
 - `ZOMBIE_TASK_TIMEOUT`: **10m**: Timeout to stop the task which have running status, but haven't been updated for a long time
 - `ENDLESS_TASK_TIMEOUT`: **3h**: Timeout to stop the tasks which have running status and continuous updates, but don't end for a long time
 - `ABANDONED_JOB_TIMEOUT`: **24h**: Timeout to cancel the jobs which have waiting status, but haven't been picked by a runner for a long time