these 2 derivations will be built:
  /nix/store/7ma9z8h1x7l0859lw9wcdx9z7b7c7cz5-nixos-test-driver-postgis.drv
  /nix/store/61fya3iyh3wyaplikj3r66lnlflm9m0a-vm-test-run-postgis.drv