(maint) Pin gems for auto release

Modeling after the learnings of the support team in commit
puppetlabs/puppetlabs-puppet_metrics_collector@78dd858

This commit pins the github_changelog_generator gem to its latest
version to make it work, and the concurrent-ruby to an older version
to compensate for the version of PDK shipped in the dev-tools
container image.

Author: mhashizume

.sync.yml

@@ -17,6 +17,9 @@ Gemfile:
         from_env: BEAKER_PUPPET_VERSION
         version: '~> 1.22'
       - gem: github_changelog_generator
+        version: '= 1.16.4'
+      - gem: concurrent-ruby
+        version: '= 1.1.10'
       - gem: async
         version: '~> 1'
       - gem: beaker-module_install_helper

Gemfile

@@ -40,7 +40,8 @@ group :development do
   gem "beaker-hostgenerator"
   gem "beaker-rspec"
   gem "beaker-puppet", *location_for(ENV['BEAKER_PUPPET_VERSION'] || '~> 1.22')
-  gem "github_changelog_generator",                                             require: false
+  gem "github_changelog_generator", '= 1.16.4',                                 require: false
+  gem "concurrent-ruby", '= 1.1.10',                                            require: false
   gem "async", '~> 1',                                                          require: false
   gem "beaker-module_install_helper",                                           require: false
   gem "beaker-puppet_install_helper",                                           require: false