Bump sphinx-github-changelog from 1.3.0 to 1.4.0

Bumps [sphinx-github-changelog](https://github.com/ewjoachim/sphinx-github-changelog) from 1.3.0 to 1.4.0.
- [Release notes](https://github.com/ewjoachim/sphinx-github-changelog/releases)
- [Changelog](https://github.com/ewjoachim/sphinx-github-changelog/blob/main/CHANGELOG.rst)
- [Commits](ewjoachim/sphinx-github-changelog@1.3.0...1.4.0)

---
updated-dependencies:
- dependency-name: sphinx-github-changelog
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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