Specify python version in flake

[LLBlumire]

When importing mach-nix with fetchGit, it's possible to set the python version with python = "python38";, there is no documentation on how to do something equivalent (if it is even possible) when working with flakes.

[waynee95]

I would like to know this too!

[TyberiusPrime]

here's how I do it

  outputs =
    { self, ..., mach-nix, pypi-deps-db, ... }:
...
        mach-nix_ = (import mach-nix) {
          inherit pkgs;
          pypiDataRev = pypi-deps-db.rev;
          pypiDataSha256 = pypi-deps-db.narHash;
          python = "python310";
        };

[TyberiusPrime]

See #556 for a full example.