Bump antora from 3.1.14 to 3.1.15

---
updated-dependencies:
- dependency-name: antora
  dependency-version: 3.1.15
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]