fix missing queue type on app.ini.sample (go-gitea#7494)

Author: lunny

custom/conf/app.ini.sample

@@ -281,7 +281,7 @@ DB_RETRY_BACKOFF = 3s
 ISSUE_INDEXER_TYPE = bleve
 ; Issue indexer storage path, available when ISSUE_INDEXER_TYPE is bleve
 ISSUE_INDEXER_PATH = indexers/issues.bleve
-; Issue indexer queue, currently support: channel or levelqueue, default is levelqueue
+; Issue indexer queue, currently support: channel, levelqueue or redis, default is levelqueue
 ISSUE_INDEXER_QUEUE_TYPE = levelqueue
 ; When ISSUE_INDEXER_QUEUE_TYPE is levelqueue, this will be the queue will be saved path,
 ; default is indexers/issues.queue