Update dependency puppet_metadata to v6

Author: renovate[bot]

Gemfile

@@ -7,7 +7,7 @@ group :test do
   gem 'voxpupuli-test', '~> 9.0',               :require => false
   gem 'coveralls',                              :require => false
   gem 'simplecov-console',                      :require => false
-  gem 'puppet_metadata', '~> 5.0',              :require => false
+  gem 'puppet_metadata', '~> 6.0',              :require => false
   gem 'puppet-lint-package_ensure-check',       :require => false
   gem 'puppet-lint-resource_reference_syntax',  :require => false
   gem 'puppet-lint-strict_indent-check',        :require => false