Fix cbbs task fail system event reference (#3571)

Author: TanGafCS

modules/system-event-reference/pages/system-event-reference.adoc

@@ -346,7 +346,7 @@ The following system events are returned for the Backup Service.
 
 | 6149 | A scheduled or one-off task has completed | Info | Cluster, repository, run type, and name.
 
-| 6150 | Cluster, repository, run type, and name. failed | Error |luster, repository, run type, name, and error message.
+| 6150 | A scheduled or one-off task has failed | Error | Cluster, repository, run type, name, and error message.
 
 | 6151 | Restore started | Info | NA