video_calls: Update do_set_zoom_token to send event on commit.

Earlier, we were using 'send_event' in 'do_set_zoom_token' which
can lead to a situation, if any db operation is added after the
'send_event' in future, where we enqueue events but the action
function fails at a later stage.

Events should not be sent until we know we're not rolling back.

Fixes part of #30489.

zerver/actions/video_calls.py

@@ -1,11 +1,14 @@
+from django.db import transaction
+
 from zerver.models import UserProfile
-from zerver.tornado.django_api import send_event
+from zerver.tornado.django_api import send_event_on_commit
 
 
+@transaction.atomic(durable=True)
 def do_set_zoom_token(user: UserProfile, token: dict[str, object] | None) -> None:
     user.zoom_token = token
     user.save(update_fields=["zoom_token"])
-    send_event(
+    send_event_on_commit(
         user.realm,
         dict(type="has_zoom_token", value=token is not None),
         [user.id],