Bump rack from 2.2.6.3 to 2.2.6.4 (#1263)

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
...

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Gemfile.lock

@@ -165,7 +165,7 @@ GEM
       pry (~> 0.10)
     public_suffix (4.0.6)
     racc (1.6.1)
-    rack (2.2.6.3)
+    rack (2.2.6.4)
     rack-test (2.0.2)
       rack (>= 1.3)
     rails (6.0.2.1)