Bump sphinx-intl from 2.3.0 to 2.3.1

Bumps [sphinx-intl](https://github.com/sphinx-doc/sphinx-intl) from 2.3.0 to 2.3.1.
- [Release notes](https://github.com/sphinx-doc/sphinx-intl/releases)
- [Changelog](https://github.com/sphinx-doc/sphinx-intl/blob/master/CHANGES.rst)
- [Commits](sphinx-doc/sphinx-intl@2.3.0...2.3.1)

---
updated-dependencies:
- dependency-name: sphinx-intl
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

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