fix: default schedule tz + migration

aircox/models/schedule.py

@@ -14,6 +14,10 @@ from .rerun import Rerun
 __all__ = ("Schedule",)
 
 
+def current_timezone_key():
+    return tz.get_current_timezone().key
+
+
 # ? BIG FIXME: self.date is still used as datetime
 class Schedule(Rerun):
     """A Schedule defines time slots of programs' diffusions.
@@ -49,7 +53,7 @@ class Schedule(Rerun):
     )
     timezone = models.CharField(
         _("timezone"),
-        default=lambda: tz.get_current_timezone().key,
+        default=current_timezone_key,
         max_length=100,
         choices=[(x, x) for x in zoneinfo.available_timezones()],
         help_text=_("timezone used for the date"),