Fix direct use of cached_property module. (#16710)

On Python 3.8 and 3.9 we use the built in functools decorator for this.

airflow/timetables/schedules.py

@@ -18,11 +18,11 @@
 import datetime
 import typing
 
-from cached_property import cached_property
 from croniter import CroniterBadCronError, CroniterBadDateError, croniter
 from dateutil.relativedelta import relativedelta
 from pendulum import DateTime
 
+from airflow.compat.functools import cached_property
 from airflow.exceptions import AirflowTimetableInvalid
 from airflow.typing_compat import Protocol
 from airflow.utils.dates import cron_presets