Bumps [actions/checkout](https://github.com/actions/checkout) from 3 to 4.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](https://github.com/actions/checkout/compare/v3...v4)

---
updated-dependencies:
- dependency-name: actions/checkout
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

news.txt is only meant as a reminder, but contributors have no way of
knowing this automatically without such a message.

The default merge branch is unreliable when trying to determine number
of commits in a PR. Using the HEAD branch of the PR removes this
ambiguity.

We seem to need the parent commit of the earliest PR commit in order to
perform common git functionality to check which files were changed.

If any commit message in the PR is either of type "feat" or is a
breaking change, then there's a high probability that news.txt should be
updated. Give an error if news.txt hasn't been updated in that case.

This workflow cannot 100% correctly determine if news.txt should be
updated even if the commit messages were exactly correct. The entries in
news.txt is determined by changes between releases, while the commit
messages are based on the master branch. While it is an approximation,
it is still a useful enough one that it's still valuable to have this
job as a reminder even if it gives an error if it shouldn't. In these
cases it is perfectly fine to ignore the failure for this job.