Unsubscribe from closed draft PR pulls

[noyoliel-devocean]

Is your feature request related to a problem? Please describe.
I open draft PRs and close them.
When the PR is closed it is published to the slack channel. This is unwanted behavior as I open and close PRs many times.
The channel is for notifying developers about PRs that require review and these notifications gives false alerts.

The channel is subscribed to 'pulls' only and the threading feature is disables

Describe the solution you'd like
ability to remove notifications about closed draft PRs

Describe alternatives you've considered
removal of github from our channel and send him links to PRs manually (which would be a shame)

Additional context
I've tried shutting down the threading feature via "/github settings" which helped remove annoying messages however there are still some remaining.