nixos/nix-channel: default to channels.nixos.org (NixOS#460057)

Author: roberth

nixos/modules/config/nix-channel.nix

@@ -71,7 +71,7 @@ in
       defaultChannel = mkOption {
         internal = true;
         type = types.str;
-        default = "https://nixos.org/channels/nixos-unstable";
+        default = "https://channels.nixos.org/nixos-unstable";
         description = "Default NixOS channel to which the root user is subscribed.";
       };
     };