[pre-commit] corner case on a PR basis

[v1v]

What

elastic/apm-integration-testing#1033 was required since elastic/apm-integration-testing#1016 was merged with a lint defect.

It was initially found and reported in the GitHub comment:

But the following commits didn't change those files and the preCommit didn't detect any failures.

Why

The preCommit step cares about the current changeset, this works well as long as the following changesets are incrementally fixing the linted issues.

But it does not work well when:

• Contributors don't use it and
• Contributors push several commits.

Then, the preCommit won't be able to fail in the following builds since the preCommit won't detect those changesets.

As a consequence, the failure will only happen in the target branch.

Proposal

preCommit should compare <target-branch>...<pr-head> rather than <target-branch>...<GIT_BASE_COMMIT

cc @elastic/observablt-robots

[v1v]

We won't invest anymore in the existing Jenkins implementation unless a security or a major bug, hence I'll close this issue now