[pygobject] tests: skip one more GdkAtom test on Windows

[Christoph Reiter <creiter src gnome org>]

commit 20fa66387020877a3ae20a6b48bba52153c7bd6c
Author: Christoph Reiter <reiter christoph gmail com>
Date:   Tue Feb 20 18:17:15 2018 +0100

    tests: skip one more GdkAtom test on Windows
    
    This has started to crash with newer gtk

 tests/test_atoms.py | 2 ++
 1 file changed, 2 insertions(+)
---
diff --git a/tests/test_atoms.py b/tests/test_atoms.py
index e1c5a897..cc8dc3c2 100644
--- a/tests/test_atoms.py
+++ b/tests/test_atoms.py
@@ -1,5 +1,6 @@
 from __future__ import absolute_import
 
+import os
 import unittest
 
 try:
@@ -43,6 +44,7 @@ class TestGdkAtom(unittest.TestCase):
 
         self.assertEqual(repr(Gdk.SELECTION_CLIPBOARD), 'Gdk.Atom.intern("CLIPBOARD", False)')
 
+    @unittest.skipUnless(os.name != "nt", "not on Windows")
     def test_in_single(self):
         a_selection = Gdk.Atom.intern('test_clipboard', False)
         clipboard = Gtk.Clipboard.get(a_selection)