Follow the sponsor directory into the pinned API error schema

The #188 merge added SponsorRevisionConflict to the APIError result
envelope (and to the published admin OpenAPI document) but missed the
pinned oneOf in test_runtime_credentials, reddening django on main in
the scheduled run at c356abe.  The pin now lists the real payload.

Refs #193

Author: alexeygrigorev

management_api/tests/test_runtime_credentials.py

@@ -372,6 +372,9 @@ def test_openapi_declares_only_real_runtime_lifecycle_contracts(self) -> None:
                 "oneOf": [
                     {"$ref": "#/components/schemas/CredentialMetadata"},
                     {"$ref": "#/components/schemas/SiteSettingRevisionConflict"},
+                    # The sponsor directory's revision conflicts ride the same
+                    # error envelope (#188); the pin follows the real payload.
+                    {"$ref": "#/components/schemas/SponsorRevisionConflict"},
                 ]
             },
         )