Best Practice for using variable in timetable seems obsolete

### What do you see as an issue? hello, it seems that the example provided in this page [https://airflow.apache.org/docs/apache-airflow/stable/best-practices.html#timetables ](https://airflow.apache.org/docs/apache-airflow/stable/best-practices.html#timetables ) is not valid anymore, not only it doesn't works but it also seems to crash dag processor <img width="585" height="72" alt="Image" src="https://github.com/user-attachments/assets/315c8bde-8989-48dc-b9d3-10165c8e7bec" /> ### Solving the problem If this example is not valid it should be removed (and maybe dag processor should not crash and provide import issue on UI) ### Anything else _No response_ ### Are you willing to submit PR? - [ ] Yes I am willing to submit a PR! ### Code of Conduct - [x] I agree to follow this project's [Code of Conduct](https://github.com/apache/airflow/blob/main/CODE_OF_CONDUCT.md)