So, if you are still stucked on Github for some reason and are impacted by the end of the "services" or simply are curious or in need to handle webhooks, here is how I did it for #YunoHost https://github.com/YunoHost/webhooks/blob/master/server.py#L32

It's very simple and straightforward. I'm using sanic but you just need to change one stuff to adapt the code for flask/quart https://github.com/YunoHost/webhooks/commit/1b522269bb6f0497e1272750f198aba6e9ebe8ad and you can subscribe to all webhooks from an organization at once (this code handle this situation). Enjoy!