python3Packages.nltk: skip failing test on darwin (#536713)

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

@@ -1,5 +1,6 @@
 {
   lib,
+  stdenv,
   pkgs,
   fetchFromGitHub,
   buildPythonPackage,
@@ -100,6 +101,11 @@ buildPythonPackage (finalAttrs: {
     "nltk/test/unit/test_downloader.py" # Touches network
   ];
 
+  disabledTests = lib.optionals stdenv.hostPlatform.isDarwin [
+    # ModuleNotFoundError: No module named '_tkinter'
+    "test_chartparser_app_uses_pickle_load_not_pickle_load_standard"
+  ];
+
   pythonImportsCheck = [ "nltk" ];
 
   passthru = {