bpo-33295: Skip test using missing external site (GH-6504) (GH-6510)

`test_urllib2net.OtherNetworkTests.test_sites_no_connection_close`
used `http://www.imdb.com/` but it is moved to https so the test is
not valid anymore.  Skip test for the moment to allow CI to proceed.
(cherry picked from commit 36d56ea8)
Co-authored-by: INADA Naoki <methane@users.noreply.github.com>

Lib/test/test_urllib2net.py

@@ -184,6 +184,7 @@ class OtherNetworkTests(unittest.TestCase):
             opener.open(request)
             self.assertEqual(request.get_header('User-agent'),'Test-Agent')
 
+    @unittest.skip('XXX: http://www.imdb.com is gone')
     def test_sites_no_connection_close(self):
         # Some sites do not send Connection: close header.
         # Verify that those work properly. (#issue12576)