This, I hope, will ensure we don't have the tested job vanish for a couple days again in the future.

This was not tested, but (1) this is the same structure of the other nixos tests with a different arg and (2) this equivalent instantiation works.

nix-instantiate --arg nixpkgs '{ outPath=./.; revCount=999999; shortRev="ofborg"; }' nixos/release-combined.nix -A tested

The name of the check is nixos as the equivalent for Darwin is simply named darwin.