Fix dead link on config flow page (#2305)

Author: IceBotYT

docs/config_entries_config_flow_handler.md

@@ -309,7 +309,7 @@ Ensuring that the `unique_id` is unchanged should be done using `await self.asyn
 ## Reauthentication
 
 Gracefully handling authentication errors such as invalid, expired, or revoked tokens is needed to advance on the [Integration Quality Scale](integration_quality_scale_index.md). This example of how to add reauth to the OAuth flow created by `script.scaffold` following the pattern in [Building a Python library](api_lib_auth.md#oauth2).
-If you are looking for how to trigger the reauthentication flow, see [handling expired credentials](integration_setup_failures#handling-expired-credentials).
+If you are looking for how to trigger the reauthentication flow, see [handling expired credentials](integration_setup_failures.md#handling-expired-credentials).
 
 This example catches an authentication exception in config entry setup in `__init__.py` and instructs the user to visit the integrations page in order to reconfigure the integration.