Bump sphinx-scylladb-theme from 1.8.10 to 1.9.1 in /docs

Bumps [sphinx-scylladb-theme](https://github.com/scylladb/sphinx-scylladb-theme) from 1.8.10 to 1.9.1.
- [Release notes](https://github.com/scylladb/sphinx-scylladb-theme/releases)
- [Commits](https://github.com/scylladb/sphinx-scylladb-theme/commits/1.9.1)

---
updated-dependencies:
- dependency-name: sphinx-scylladb-theme
  dependency-version: 1.9.1
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

docs/poetry.lock

@@ -9,7 +9,7 @@ package-mode = false
 python = "^3.13"
 pygments = "^2.19.2"
 redirects_cli = "^0.1.3"
-sphinx-scylladb-theme = "^1.8.10"
+sphinx-scylladb-theme = "^1.9.1"
 sphinx-sitemap = "^2.8.0"
 sphinx-autobuild = "^2025.0.0"
 Sphinx = "^8.0.0"