fix(login): include background task id in auth test

Set `background_task_id` on the dummy ChatGPT auth fixture so Bazel can compile the login test target after the auth record shape changed upstream.

codex-rs/login/src/auth/auth_tests.rs

@@ -243,6 +243,7 @@ fn dummy_chatgpt_auth_does_not_create_cwd_auth_json_when_identity_is_set() {
         agent_runtime_id: "agent_123".to_string(),
         agent_private_key: "pkcs8-base64".to_string(),
         registered_at: "2026-04-13T12:00:00Z".to_string(),
+        background_task_id: None,
     };
 
     auth.set_agent_identity(record.clone())