When editing the first post for the topic we do two AJAX requests
to two separate controllers in this order:
PUT /t/topic-name
PUT /posts/2489523
This causes two post revisor calls, which end up triggering the
:post_edited DiscourseEvent twice. This is then picked up and sent
as a WebHook event twice. However we do not need to send a :post_edited
webhook event if the first post is being edited and topic_changed is
true from the :post_edited DiscourseEvent, because a second event will
shortly come through for just the post.
See https://meta.discourse.org/t/post-webhook-fires-two-times-on-post-edited-for-first-post-in-a-topic/162408
Continued on from https://github.com/discourse/discourse/pull/10590
292017dd25