Changes

Changelog checks are failing on a recent PR with an error saying no changelog file has been added. The PR however has added a changelog file.

The error is occurring because the changelog workflow is comparing the PR's branch against origin/main directly. When a branch is not up to date with main, as is the case with the referenced PR, files added to main that aren't in the PR's branch show up as renamed in git, rather than new files. The check then fails because no new files were detected.

The solution here is to compare the PR's branch to the best common ancestor (git merge-base) with origin/main. This takes into account the branch being out of date and properly detects new files.

Note that this change is simply being copied over from opentelemetry-collector and opentelemetry-collector-contrib

Merge requirement checklist

• CONTRIBUTING.md guidelines followed.
• Change log entry added, according to the guidelines in When to add a changelog entry.
  • If your PR does not need a change log, start the PR title with [chore]
• schema-next.yaml updated with changes to existing conventions.