Bump parallel_tests from 2.21.2 to 2.21.3 in /Library/Homebrew/test

Bumps [parallel_tests](https://github.com/grosser/parallel_tests) from 2.21.2 to 2.21.3.
- [Release notes](https://github.com/grosser/parallel_tests/releases)
- [Commits](https://github.com/grosser/parallel_tests/compare/v2.21.2...v2.21.3

)

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

Library/Homebrew/test/Gemfile.lock

@@ -10,7 +10,7 @@ GEM
     docile (1.3.0)
     json (2.1.0)
     parallel (1.12.1)
-    parallel_tests (2.21.2)
+    parallel_tests (2.21.3)
       parallel
     parser (2.5.0.5)
       ast (~> 2.4.0)