Bump nokogiri from 1.15.5 to 1.15.6 in /docs

Bumps [nokogiri](https://github.com/sparklemotion/nokogiri) from 1.15.5 to 1.15.6.
- [Release notes](https://github.com/sparklemotion/nokogiri/releases)
- [Changelog](https://github.com/sparklemotion/nokogiri/blob/main/CHANGELOG.md)
- [Commits](sparklemotion/nokogiri@v1.15.5...v1.15.6)

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

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

docs/Gemfile.lock

@@ -214,7 +214,7 @@ GEM
       jekyll-feed (~> 0.9)
       jekyll-seo-tag (~> 2.1)
     minitest (5.20.0)
-    nokogiri (1.15.5)
+    nokogiri (1.15.6)
       mini_portile2 (~> 2.8.2)
       racc (~> 1.4)
     octokit (4.25.1)