Use transaction decorator on group accept

bookwyrm/models/group.py

@@ -150,10 +150,9 @@ class GroupMemberInvitation(models.Model):
             notification_type=notification_type,
         )
 
+    @transaction.atomic
     def accept(self):
         """turn this request into the real deal"""
-
-        with transaction.atomic():
         GroupMember.from_request(self)
 
         model = apps.get_model("bookwyrm.Notification", require_ready=True)