fix python 3.8 compat for edoxid calendar sync

apache/airflow:2.7.1 base image ships Python 3.8, which doesn't have
zoneinfo (3.9+) and can't evaluate `X | Y` / list[X] type hints at
runtime (3.10+). Add `from __future__ import annotations` everywhere
and swap zoneinfo -> pytz (already a dependency in this repo).

scripts/edoxid_calendar_database.py

@@ -1,3 +1,5 @@
+from __future__ import annotations
+
 from datetime import date, datetime
 
 import pymysql