Bump rack from 2.2.6.3 to 2.2.6.4

Bumps [rack](https://github.com/rack/rack) from 2.2.6.3 to 2.2.6.4.
- [Release notes](https://github.com/rack/rack/releases)
- [Changelog](https://github.com/rack/rack/blob/main/CHANGELOG.md)
- [Commits](rack/rack@v2.2.6.3...v2.2.6.4)

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

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

Author: dependabot[bot]

Gemfile.lock

@@ -87,7 +87,7 @@ GEM
     puma (4.3.12)
       nio4r (~> 2.0)
     racc (1.6.1)
-    rack (2.2.6.3)
+    rack (2.2.6.4)
     rack-test (1.1.0)
       rack (>= 1.0, < 3)
     rails (5.2.0)