ci docker runner puppet catalog broken

this affects both ci-runner-01 and ci-runner-arm64-02.torproject.org, but somehow not chi-node-14:

Error: Could not retrieve catalog from remote server: Error 500 on SERVER: Server Error: Evaluation Error: Error while evaluating a Method call, 'reduce' expects one of:
  (Iterable enumerable, Callable[2, 2] block)
    rejected: expects 1 argument, got 2
  (Iterable enumerable, Any memo, Callable[2, 2] block)
    rejected: parameter 'enumerable' expects an Iterable value, got Undef (file: /srv/puppet.torproject.org/stages/production/modules/profile/manifests/gitlab/runner.pp, line: 29, column: 30) on node ci-runner-01.torproject.org
Warning: Not using cache on failed catalog
Error: Could not retrieve catalog; skipping run

this was probably introduced by @lavamind recently...