docs: Fix URL for Github callback in OAuth. (#41122)

docs/sources/auth/github.md

@@ -16,7 +16,7 @@ settings page). When you create the application you will need to specify
 a callback URL. Specify this as callback:
 
 ```bash
-http://<my_grafana_server_name_or_ip>:<grafana_server_port>/login/github
+http://<my_grafana_server_name_or_ip>:<grafana_server_port>/grafana/login/github
 ```
 
 This callback URL must match the full HTTP address that you use in your