chore: cancel old in-progress CI workflows

[littledivy]

CI will run only on the latest commit in a PR. Saves energy 🌲

https://docs.github.com/en/actions/using-workflows/workflow-syntax-for-github-actions#concurrency

Idea from nodejs/node#42017

[kt3k]

LGTM. Nice!

[lucacasonato]

Can we not do this on main? On main we want CI for every commit so we get all the canary releases.

[kt3k]

@lucacasonato
github doc says github.head_ref is only defined on pull_request events. So the expression ${{ github.head_ref || github.run_id }} should fallback to github.run_id (unique for each run) at push event, and won't prevent the main build (to my understanding)

[littledivy]

Yup, This won't affect main since concurrency group github.run_id is always unique

[lucacasonato]

One note: this does make committing multiple commits to find flaky tests more difficult.

[bartlomieju]

One note: this does make committing multiple commits to find flaky tests more difficult.

Yeah basically in such case we'll need to push empty commit after the previous one finished. Let's see how it works, but I'm skeptical