Bump github-label-sync from 2.2.0 to 2.3.1

Bumps [github-label-sync](https://github.com/Financial-Times/github-label-sync) from 2.2.0 to 2.3.1.
- [Release notes](https://github.com/Financial-Times/github-label-sync/releases)
- [Changelog](https://github.com/Financial-Times/github-label-sync/blob/master/CHANGELOG.md)
- [Commits](Financial-Times/github-label-sync@v2.2.0...v2.3.1)

---
updated-dependencies:
- dependency-name: github-label-sync
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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Author: dependabot[bot]