Upgrade Nix version

[dsalaza4]

Makes currently uses Nix 2.15: https://github.com/fluidattacks/makes/blob/main/makes/cli/env/runtime/main.nix#L9

Newest version is: https://nixos.org/download/#

Let's upgrade it

[dsalaza4]

This would probably also require upgrading __nixpkgs__

[rohaquinlop]

First I'll deprecate node2nix #1378 and keep working on this issue, then will drop nodejs 21 #1373