Force usage of pytz

For timezone functionalities icalendar can use both pytz and zoneinfo,
preferring zoneinfo.

We rely on pytz for several attributes, stick to it.

Fixes pimutils#1361.
Should obsolete pimutils#1363.

Author: iamleot

CHANGELOG.rst

@@ -7,6 +7,11 @@ Package maintainers and users who have to manually update their installation
 may want to subscribe to `GitHub's tag feed
 <https://github.com/geier/khal/tags.atom>`_.
 
+0.13.0
+======
+unreleased
+* UPDATED REQUIREMENT icalendar is now required >= 6.0.0
+
 0.12.0
 ======
 2025-04-14

khal/icalendar.py

@@ -37,6 +37,10 @@
 
 logger = logging.getLogger('khal')
 
+# Force use of pytz because we rely on functionalities not available in
+# zoneinfo.
+icalendar.use_pytz()
+
 
 def split_ics(ics: str, random_uid: bool=False, default_timezone=None) -> list:
     """split an ics string into several according to VEVENT's UIDs

pyproject.toml

@@ -27,7 +27,7 @@ requires-python = ">=3.9,<3.14"
 dependencies = [
     "click>=3.2",
     "click_log>=0.2.0",
-    "icalendar>=4.0.3,<6.0.0",
+    "icalendar>=6.0.0",
     "urwid>=2.6.15",
     "pyxdg",
     "pytz",