Feature idea: check multiple nixpkgs

[dpc]

It's quite common for our project to need something from nixpkgs-unstable, while we prefer to stick with nixpkgs/nixos-xx.yy for everything else. So we import nixpkgs twice (actually 3 times, for reasons...) and mix and match.

Anyway - would be nice if we could check multiple/other inputs as well.

[lucperkins]

@dpc This is actually already possible 😄 You can run this in that repo:

flake-checker --nixpkgs-keys nixpkgs,nixpkgs-unstable,nixpkgs-kitman

And in the Action you can use the nixpkgs-keys config.