BIG UPD: migrate to python 3.10 and django 3.2

dav_events/models/eventflag.py

@@ -2,7 +2,6 @@ from __future__ import unicode_literals
 from django.conf import settings
 from django.db import models
 from django.utils import timezone
-from django.utils.encoding import python_2_unicode_compatible
 
 from . import get_ghost_user, get_system_user
 
@@ -11,9 +10,8 @@ def get_system_user_id():
     return get_system_user().id
 
 
-@python_2_unicode_compatible
 class EventFlag(models.Model):
-    event = models.ForeignKey('dav_events.Event', related_name='flags')
+    event = models.ForeignKey('dav_events.Event', related_name='flags', on_delete=models.CASCADE)
     status = models.ForeignKey('dav_events.EventStatus',
                                on_delete=models.PROTECT,
                                related_name='+')