test_urllibnet: set timeout on test_fileno()

Use the default timeout of 30 seconds to avoid blocking forever.

Lib/test/test_urllibnet.py

@@ -104,7 +104,7 @@ class urlopenNetworkTests(unittest.TestCase):
     @unittest.skipIf(sys.platform in ('win32',), 'not appropriate for Windows')
     def test_fileno(self):
         # Make sure fd returned by fileno is valid.
-        with self.urlopen("http://www.google.com/", timeout=None) as open_url:
+        with self.urlopen("http://www.google.com/") as open_url:
             fd = open_url.fileno()
             with os.fdopen(fd, 'rb') as f:
                 self.assertTrue(f.read(), "reading from file created using fd "