build(deps): bump rack from 3.0.8 to 3.0.9.1 in /functions/slack (#1322)

Bumps [rack](https://github.com/rack/rack) from 3.0.8 to 3.0.9.1.
- [Release notes](https://github.com/rack/rack/releases)
- [Changelog](https://github.com/rack/rack/blob/main/CHANGELOG.md)
- [Commits](rack/rack@v3.0.8...v3.0.9.1)

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

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

functions/slack/Gemfile.lock

@@ -49,7 +49,7 @@ GEM
     public_suffix (5.0.3)
     puma (6.4.2)
       nio4r (~> 2.0)
-    rack (3.0.8)
+    rack (3.0.9.1)
     representable (3.2.0)
       declarative (< 0.1.0)
       trailblazer-option (>= 0.1.1, < 0.2.0)