Bump nokogiri from 1.18.8 to 1.18.9 in /demo

Bumps [nokogiri](https://github.com/sparklemotion/nokogiri) from 1.18.8 to 1.18.9.
- [Release notes](https://github.com/sparklemotion/nokogiri/releases)
- [Changelog](https://github.com/sparklemotion/nokogiri/blob/main/CHANGELOG.md)
- [Commits](sparklemotion/nokogiri@v1.18.8...v1.18.9)

---
updated-dependencies:
- dependency-name: nokogiri
  dependency-version: 1.18.9
  dependency-type: indirect
...

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

Author: dependabot[bot]

demo/Gemfile.lock

@@ -243,11 +243,11 @@ GEM
     mutex_m (0.3.0)
     netrc (0.11.0)
     nio4r (2.7.4)
-    nokogiri (1.18.8-arm64-darwin)
+    nokogiri (1.18.9-arm64-darwin)
       racc (~> 1.4)
-    nokogiri (1.18.8-x86_64-darwin)
+    nokogiri (1.18.9-x86_64-darwin)
       racc (~> 1.4)
-    nokogiri (1.18.8-x86_64-linux-gnu)
+    nokogiri (1.18.9-x86_64-linux-gnu)
       racc (~> 1.4)
     octicons (19.15.3)
     oj (3.16.10)