python3Packages.dulwich: re-enable darwin tests (#423572)

pkgs/development/python-modules/dulwich/default.nix

···
     "tests/contrib/test_swift_smoke.py"
   ];
 
-  doCheck = !stdenv.hostPlatform.isDarwin;
+  __darwinAllowLocalNetworking = true;
 
   pythonImportsCheck = [ "dulwich" ];