nixos/macos-builder: pin `stateVersion` (#342380)

      # To prevent gratuitous rebuilds on each change to Nixpkgs

      nixos.revision = null;

      stateVersion = lib.mkDefault (throw ''

        The macOS linux builder should not need a stateVersion to be set, but a module

        has accessed stateVersion nonetheless.

        Please inspect the trace of the following command to figure out which module

        has a dependency on stateVersion.

          nix-instantiate --attr darwin.linux-builder --show-trace

      '');

      # to be updated by module maintainers, see nixpkgs#325610

      stateVersion = "24.05";

    };

    users.users."${user}" = {