test: verify signup_start response only contains email

backend/tests/integration/test_auth_routes.py

@@ -103,8 +103,7 @@ def test_signup_start_returns_pending_response() -> None:
             },
         )
         assert response.status_code == 202
-        body = response.json()
-        assert body["email"] == "user@example.com"
+        assert response.json() == {"email": "user@example.com"}
     finally:
         app.dependency_overrides = {}