Bump rack from 2.1.2 to 2.2.3 in /spec/integration/rails_6.0.2.1 (#819)

Bumps [rack](https://github.com/rack/rack) from 2.1.2 to 2.2.3.
- [Release notes](https://github.com/rack/rack/releases)
- [Changelog](https://github.com/rack/rack/blob/master/CHANGELOG.md)
- [Commits](rack/rack@2.1.2...2.2.3)

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Author: dependabot[bot]

spec/integration/rails_6.0.2.1/Gemfile.lock

@@ -112,7 +112,7 @@ GEM
     public_suffix (4.0.3)
     puma (4.3.5)
       nio4r (~> 2.0)
-    rack (2.1.2)
+    rack (2.2.3)
     rack-test (1.1.0)
       rack (>= 1.0, < 3)
     rails (6.0.2.1)