Bump rack from 2.0.8 to 2.2.3 in /apps/epp_proxy/priv/test_backend_app

Bumps [rack](https://github.com/rack/rack) from 2.0.8 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@2.0.8...2.2.3)

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

Author: dependabot[bot]

apps/epp_proxy/priv/test_backend_app/Gemfile.lock

@@ -4,7 +4,7 @@ GEM
     nio4r (2.5.2)
     puma (4.3.5)
       nio4r (~> 2.0)
-    rack (2.0.8)
+    rack (2.2.3)
     rack-unreloader (1.7.0)
     roda (3.21.0)
       rack