cask-tests: fix cask-tests always fail on the test failure

`brew cask-tests` collected the test results in an improper way so that it reports a false success in certain situations.
Specially, the session under BrewTestBot always reports success regardless of the test status.
With this update, the exit code of `brew cask-tests` is 1 when the test fails, and then CI preperly works.

Library/Homebrew/cask/cmd/brew-cask-tests.rb

@@ -26,6 +26,8 @@ repo_root.cd do
 
   ENV["HOMEBREW_TESTS_COVERAGE"] = "1" if ARGV.flag?("--coverage")
 
+  failed = false
+
   if rspec
     run_tests "parallel_rspec", Dir["spec/**/*_spec.rb"], %w[
       --color
@@ -34,15 +36,17 @@ repo_root.cd do
       --format ParallelTests::RSpec::RuntimeLogger
       --out tmp/parallel_runtime_rspec.log
     ]
+    failed ||= !$CHILD_STATUS.success?
   end
 
   if minitest
     run_tests "parallel_test", Dir["test/**/*_test.rb"]
+    failed ||= !$CHILD_STATUS.success?
   end
 
+  Homebrew.failed = failed
+
   if ENV["CODECOV_TOKEN"]
     system "bundle", "exec", "rake", "test:coverage:upload"
   end
-
-  Homebrew.failed = !$CHILD_STATUS.success?
 end