chore(deps): bump rack from 3.0.16 to 3.1.18 in /images/fluentd/outputs

Bumps [rack](https://github.com/rack/rack) from 3.0.16 to 3.1.18.
- [Release notes](https://github.com/rack/rack/releases)
- [Changelog](https://github.com/rack/rack/blob/main/CHANGELOG.md)
- [Commits](rack/rack@v3.0.16...v3.1.18)

---
updated-dependencies:
- dependency-name: rack
  dependency-version: 3.1.18
  dependency-type: indirect
...

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

Author: dependabot[bot]

images/fluentd/outputs/Gemfile.lock

@@ -364,7 +364,7 @@ GEM
       protocol-http (~> 0.47)
     public_suffix (5.0.3)
     racc (1.8.1)
-    rack (3.0.16)
+    rack (3.1.18)
     rack-oauth2 (1.21.3)
       activesupport
       attr_required