Replaced ugettext and ugettext_lazy with gettext and gettext_lazy

ugettext and ugettext_lazy were deprecated in Django 3 and will be
removed in Django 4.

dav_events/views/events.py

@@ -14,7 +14,7 @@ from django.shortcuts import get_object_or_404
 from django.urls import reverse, reverse_lazy
 from django.utils.decorators import method_decorator
 from django.utils.text import normalize_newlines
-from django.utils.translation import ugettext as _
+from django.utils.translation import gettext as _
 from django.views import generic
 
 from .. import choices