nix/key: add dyndnsKey

nix/key/flake.nix

@@ -3,5 +3,7 @@
 
   outputs = { ... }: {
     lib.gpgKey = null;
+    # test key
+    lib.dyndnsKey = "Dr1QHSfNtAwgbdoNBtCgl5NxsSXlaw9+qo7juiVTv58=";
   };
 }