Use hiera_config in .sync.yml

[ekohl]

[vox-pupuli-tasks[bot]]

Dear @ekohl, thanks for the PR!

This is Vox Pupuli Tasks, your friendly Vox Pupuli Github Bot. I noticed that your pull request has CI failures. Can you please have a look at the failing CI jobs? If you need any help, you can reach out to us on our IRC channel voxpupuli on Freenode or our Slack channel voxpupuli at slack.puppet.com. You can find my sourcecode at voxpupuli/vox-pupuli-tasks