CI/CD Github mirroring doesn't trigger on_stop for branch deletion

Summary

While mirroring a github repo for CI/CD, deleting a branch does not trigger the on_stop job

Steps to reproduce

• Create a github project
• Create a gitlab project that mirrors the github project
• Create a pipeline which includes a job with environment and another job using the same environment and with a on_stop
• Witness the on_stop job not being triggered on branch deletion

What is the current bug behavior?

• The job isn't triggered even though the branch has been deleted

What is the expected correct behavior?

• The job should be triggered on branch deletion