configuration/common: force reigistry pinning for nixpkgs

configuration/common/default.nix

@@ -116,7 +116,7 @@
   # Pin current nixpkgs channel and flake registry to the nixpkgs version
   # the host got build with
   nix.nixPath = lib.mkForce [ "nixpkgs=${lib.cleanSource pkgs.path}" ];
-  nix.registry = {
+  nix.registry = lib.mkForce {
     "nixpkgs" = {
        from = {
          type = "indirect";