CI should not run on draft PRs, closing pull request should cancel outstanding CI run

[nchaimov]

1. Currently, the CI workflow tries to run (and requests review) in all PRs, including draft PRs. Instead, don't run CI until marked ready for review. Relevant discussion here: https://github.com/orgs/community/discussions/120231
2. Currently, closing a PR with waiting, unreviewed CI workflows leaves the request for review open. Instead, cancel waiting workflows when the associated PR is closed. Relevant discussion here: https://github.com/orgs/community/discussions/62390