Bump rack from 2.2.4 to 2.2.6.4

Bumps [rack](https://github.com/rack/rack) from 2.2.4 to 2.2.6.4.
- [Release notes](https://github.com/rack/rack/releases)
- [Changelog](https://github.com/rack/rack/blob/main/CHANGELOG.md)
- [Commits](https://github.com/rack/rack/compare/2.2.4...v2.2.6.4)

---
updated-dependencies:
- dependency-name: rack
  dependency-type: indirect
...
Signed-off-by: Ndependabot[bot] <support@github.com>

Gemfile.lock

@@ -33,7 +33,7 @@ GEM
     multi_test (0.1.2)
     mustermann (2.0.2)
       ruby2_keywords (~> 0.0.1)
-    rack (2.2.4)
+    rack (2.2.6.4)
     rack-protection (2.2.3)
       rack
     rspec-expectations (3.11.0)