Bump actions/checkout from 4 to 6

Bumps [actions/checkout](https://github.com/actions/checkout) from 4 to 6.
- [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/v4...v6)

---
updated-dependencies:
- dependency-name: actions/checkout
  dependency-version: '6'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

Enable Dependabot for GH Actions

bump GitPython and Python

Python 3.13 support

CI update

Add Python 3.12 and remove unsupported versions

Python 3.11 CI build

Add CodeQL, dependency review gh actions

Github Action CI migration

Travis CI

Support simple comments in the bookmarks file

Put it in a better place...

Accessed by _load_config_file()