`release.py abandon` deleted the draft and wrote the marker but left the
attempt's Stable Release run going. A live run keeps building, and with
autopublish on it can publish the draft that abandon just cleared.
abandon now lists the claim ref's runs of stable-release.yml and runs
`gh run cancel <id> --force` on every one that has not completed. This
happens before the draft is deleted and before the marker is written: the
marker removes the attempt from the outstanding set, so a cancel failure
after it could never be retried. A published release is still refused
before anything is cancelled. The `delete` callable is renamed `execute`
since it now runs cancels too.