Update docs/en/latest/plugins/forward-auth.md

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: Yilialinn

docs/en/latest/plugins/forward-auth.md

@@ -1161,7 +1161,7 @@ curl -i "http://127.0.0.1:9080/post" -X POST -d '
 
 You should receive an `HTTP/1.1 200 OK` response.
 
-Send a POST request with `tenant_id` in the body:
+Send a POST request with an invalid `tenant_id` in the body:
 
 ```shell
 curl -i "http://127.0.0.1:9080/post" -X POST -d '