On 24.10 (Electric Eel) credentials["provider"] is the type string with
account/key in credentials["attributes"]; 25.04+ moved them into a
provider dict. The injected get_restic_config only handled the newer
shape and raised TypeError on 24.10 at task creation (#1).
The method now detects the schema and reads credentials from the right
place on both. create_task.py list-credentials and list-tasks use the
same schema-agnostic lookup.