This fixes a bug where nixos-rebuild as root cannot build a nixos
configuration since it cannot fetch the sources of our fork of
nix-eval-jobs for lack of ssh key. It doesn't hit cache *in the store*
for lack of `narHash` being specified, which cannot be specified with
npins since npins doesn't output SRI hashes for git inputs.
Altogether a very silly situation. Clearly we just need another pinning
tool.
