dnstake: mark as broken on darwin

pkgs/by-name/dn/dnstake/package.nix

···
 {
   lib,
+  stdenv,
   buildGoModule,
   fetchFromGitHub,
 }:
···
     license = licenses.mit;
     maintainers = with maintainers; [ fab ];
     mainProgram = "dnstake";
+    broken = stdenv.hostPlatform.isDarwin;
   };
 }