Bump nokogiri from 1.13.6 to 1.13.9 in /docs

Bumps [nokogiri](https://github.com/sparklemotion/nokogiri) from 1.13.6 to 1.13.9.
- [Release notes](https://github.com/sparklemotion/nokogiri/releases)
- [Changelog](https://github.com/sparklemotion/nokogiri/blob/main/CHANGELOG.md)
- [Commits](sparklemotion/nokogiri@v1.13.6...v1.13.9)

---
updated-dependencies:
- dependency-name: nokogiri
  dependency-type: indirect
...

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

Author: dependabot[bot]

docs/Gemfile.lock

@@ -223,11 +223,11 @@ GEM
       jekyll-seo-tag (~> 2.1)
     minitest (5.14.4)
     multipart-post (2.1.1)
-    nokogiri (1.13.6-arm64-darwin)
+    nokogiri (1.13.9-arm64-darwin)
       racc (~> 1.4)
-    nokogiri (1.13.6-x86_64-darwin)
+    nokogiri (1.13.9-x86_64-darwin)
       racc (~> 1.4)
-    nokogiri (1.13.6-x86_64-linux)
+    nokogiri (1.13.9-x86_64-linux)
       racc (~> 1.4)
     octokit (4.21.0)
       faraday (>= 0.9)