these 2 derivations will be built:
  /nix/store/fzdyr9mspkk22kpshdzrc74y2f9z2rxa-nixos-test-driver-pg_cron.drv
  /nix/store/iflxhvx784crgg2idsp2mavc7i3hs01v-vm-test-run-pg_cron.drv