bpo-40275: Move transient_internet from test.support to socket_helper (GH-19711)

diff --git a/Lib/test/test_socket.py b/Lib/test/test_socket.py
index a70e282..87ae2e1 100755
--- a/Lib/test/test_socket.py
+++ b/Lib/test/test_socket.py
@@ -1533,7 +1533,7 @@
     def test_idna(self):
         # Check for internet access before running test
         # (issue #12804, issue #25138).
-        with support.transient_internet('python.org'):
+        with socket_helper.transient_internet('python.org'):
             socket.gethostbyname('python.org')
 
         # these should all be successful