CI: Cancelling outdated builds

Stream: mathlib4

[Moritz Doll]

In mathlib3 CI only built the most current commit on each branch, so if you pushed a new commit, the build of the old commit would get cancelled. At the moment this is probably very low priority, but I think it would be good if this is also done for mathlib4.

[Scott Morrison]

I'm pretty sure it already happens?

[Scott Morrison]

Oh! Apparently not. https://github.com/leanprover-community/mathlib4/pull/1037

[Scott Morrison]

Hmm, this doesn't seem to work. I pushed two commits in quick succession, but the second one says:

Run styfle/cancel-workflow-action@0.9.0
{
  eventName: 'push',
  sha: '0d8621d97f1b0eebd038bb24eae6278242e297e1',
  headSha: '0d8621d97f1b0eebd038bb24eae6278242e297e1',
  branch: 'cancel_runs',
  owner: 'leanprover-community',
  repo: 'mathlib4',
  GITHUB_RUN_ID: '3700529723'
}
Found token: yes
Found workflow_id: ["31072709"]
Found 3 runs total.
Found 0 runs to cancel.

Cancel Complete.

[Scott Morrison]

Oh, hmm, they seem to be cancelling now.