bpo-40275: Use new test.support helper submodules in tests (GH-20824)

diff --git a/Lib/test/test_xmlrpc.py b/Lib/test/test_xmlrpc.py
index 79f702d..3dfa84b 100644
--- a/Lib/test/test_xmlrpc.py
+++ b/Lib/test/test_xmlrpc.py
@@ -15,6 +15,7 @@
 import io
 import contextlib
 from test import support
+from test.support import os_helper
 from test.support import socket_helper
 from test.support import threading_helper
 from test.support import ALWAYS_EQ, LARGEST, SMALLEST
@@ -1372,7 +1373,7 @@
         self.cgi = None
 
     def test_cgi_get(self):
-        with support.EnvironmentVarGuard() as env:
+        with os_helper.EnvironmentVarGuard() as env:
             env['REQUEST_METHOD'] = 'GET'
             # if the method is GET and no request_text is given, it runs handle_get
             # get sysout output
@@ -1404,7 +1405,7 @@
         </methodCall>
         """
 
-        with support.EnvironmentVarGuard() as env, \
+        with os_helper.EnvironmentVarGuard() as env, \
              captured_stdout(encoding=self.cgi.encoding) as data_out, \
              support.captured_stdin() as data_in:
             data_in.write(data)