knot-dns: fix darwin build by allowing local networking in the sandbox (#399240)

pkgs/by-name/kn/knot-dns/package.nix

@@ -101,6 +101,8 @@ stdenv.mkDerivation rec {
     "-DNDEBUG"
   ];
 
+  __darwinAllowLocalNetworking = true;
+
   doCheck = true;
   checkFlags = [ "V=1" ]; # verbose output in case some test fails
   doInstallCheck = true;