For posterity, this fixes these kind of forking errors when managing the state of the agent service using a `service` resource:
Jun 2515:41:37 pe-201970-compile puppet-agent[9133]: Run of Puppet configuration client already in progress; skipping (/opt/puppetlabs/puppet/cache/state/agent_catalog_run.lock exists)
Jun 2515:41:37 pe-201970-compile puppet: /opt/puppetlabs/puppet/lib/ruby/vendor_ruby/puppet/agent.rb:94:in `fork': unexpected return