add correct config item in comment (#22393) (#22493)

Author: ti-chi-bot

dynamic-config.md

@@ -93,7 +93,7 @@ If an error occurs during the batch modification, a warning is returned:
 {{< copyable "sql" >}}
 
 ```sql
-set config tikv `log-level`='warn';
+set config tikv `log-level`='warn'; -- This command fails because `log-level` is incorrect. Use `log.level` instead.
 ```
 
 ```sql