Bump rack-attack from 6.3.1 to 6.4.0 (#15628)

Bumps [rack-attack](https://github.com/rack/rack-attack) from 6.3.1 to 6.4.0.
- [Release notes](https://github.com/rack/rack-attack/releases)
- [Changelog](https://github.com/rack/rack-attack/blob/master/CHANGELOG.md)
- [Commits](https://github.com/rack/rack-attack/compare/v6.3.1...v6.4.0)

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

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

Gemfile.lock

@@ -436,7 +436,7 @@ GEM
     raabro (1.3.3)
     racc (1.5.2)
     rack (2.2.3)
-    rack-attack (6.3.1)
+    rack-attack (6.4.0)
       rack (>= 1.0, < 3)
     rack-cors (1.1.1)
       rack (>= 2.0.0)
@@ -772,7 +772,7 @@ DEPENDENCIES
   puma (~> 5.1)
   pundit (~> 2.1)
   rack (~> 2.2.3)
-  rack-attack (~> 6.3)
+  rack-attack (~> 6.4)
   rack-cors (~> 1.1)
   rails (~> 5.2.4.4)
   rails-controller-testing (~> 1.0)