Bump sphinx-scylladb-theme from 1.8.5 to 1.8.6 in /docs

Bumps [sphinx-scylladb-theme](https://github.com/scylladb/sphinx-scylladb-theme) from 1.8.5 to 1.8.6.
- [Release notes](https://github.com/scylladb/sphinx-scylladb-theme/releases)
- [Commits](scylladb/sphinx-scylladb-theme@1.8.5...1.8.6)

---
updated-dependencies:
- dependency-name: sphinx-scylladb-theme
  dependency-version: 1.8.6
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]