Revert "First steps into pytz deprecation"

This reverts commit e4e7d50659.

src/pretix/control/views/dashboards.py

@@ -34,8 +34,8 @@
 
 from datetime import timedelta
 from decimal import Decimal
-from zoneinfo import ZoneInfo
 
+import pytz
 from django.conf import settings
 from django.contrib.contenttypes.models import ContentType
 from django.db.models import (
@@ -510,7 +510,7 @@ def widgets_for_event_qs(request, qs, user, nmax, lazy=False):
     for event in events:
         if not lazy:
             tzname = event.cache.get_or_set('timezone', lambda: event.settings.timezone)
-            tz = ZoneInfo(tzname)
+            tz = pytz.timezone(tzname)
             if event.has_subevents:
                 if event.min_from is None:
                     dr = pgettext("subevent", "No dates")