test flake: clean up, use coreutils instead of busybox for macOS support

tests/flake.nix

@@ -1,17 +1,15 @@
 {
-  inputs.nixpkgs.url = "github:NixOS/nixpkgs/release-24.05";
-
   inputs.flake-utils.url = "github:numtide/flake-utils";
+  inputs.nixpkgs.url = "github:NixOS/nixpkgs/release-24.05";
 
-  outputs = { self, nixpkgs, flake-utils }@inputs:
-    # flake-utils.lib.eachDefaultSystem (system:
+  outputs = { self, flake-utils, nixpkgs }:
     flake-utils.lib.eachSystem ["x86_64-linux" "x86_64-darwin" "aarch64-darwin"] (system:
       let
         pkgs = import nixpkgs { inherit system; };
         tests = pkgs.haskell.packages.ghc965.callPackage ./tests.nix {};
       in
         rec {
-          packages = rec {
+          packages = {
             inherit tests;
             inherit (pkgs) cabal2nix;
 
@@ -20,7 +18,7 @@
             # Print a trivial PATH that we can use to run kernel and LSP tests, to ensure
             # they aren't depending on anything on the test machine's PATH.
             print-basic-path = pkgs.writeShellScriptBin "codedown-artifact-sizes.sh" ''
-              echo ${pkgs.lib.makeBinPath (with pkgs; [busybox bash])}
+              echo ${pkgs.lib.makeBinPath (with pkgs; [coreutils bash])}
             '';
           };