Bump antora from 3.1.7 to 3.1.8

Bumps [antora](https://gitlab.com/antora/antora) from 3.1.7 to 3.1.8.
- [Changelog](https://gitlab.com/antora/antora/blob/main/CHANGELOG.adoc)
- [Commits](https://gitlab.com/antora/antora/compare/v3.1.7...v3.1.8)

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

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