nixos/guix: set proxy env vars for guix-daemon (#373948)

        # It's similar to Nix daemon so there's no question whether or not this

        # should be sandboxed.

        systemd.services.guix-daemon = {

          environment = serviceEnv;

          environment = serviceEnv // config.networking.proxy.envVars;

          script = ''

            exec ${lib.getExe' package "guix-daemon"} \

              --build-users-group=${cfg.group} \