chore(deps): bump nokogiri in /images/fluentd/outputs

Bumps [nokogiri](https://github.com/sparklemotion/nokogiri) from 1.18.4 to 1.18.8.
- [Release notes](https://github.com/sparklemotion/nokogiri/releases)
- [Changelog](https://github.com/sparklemotion/nokogiri/blob/main/CHANGELOG.md)
- [Commits](sparklemotion/nokogiri@v1.18.4...v1.18.8)

---
updated-dependencies:
- dependency-name: nokogiri
  dependency-version: 1.18.8
  dependency-type: indirect
...

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

Author: dependabot[bot]

images/fluentd/outputs/Gemfile.lock

@@ -283,7 +283,7 @@ GEM
     net-smtp (0.4.0)
       net-protocol
     netrc (0.11.0)
-    nokogiri (1.18.4)
+    nokogiri (1.18.8)
       mini_portile2 (~> 2.8.2)
       racc (~> 1.4)
     oj (3.16.10)