bpo-40275: Use new test.support helper submodules in tests (GH-21743)

Lib/tkinter/test/test_tkinter/test_loadtk.py

@@ -2,6 +2,7 @@ import os
 import sys
 import unittest
 import test.support as test_support
+from test.support import os_helper
 from tkinter import Tcl, TclError
 
 test_support.requires('gui')
@@ -24,7 +25,7 @@ class TkLoadTest(unittest.TestCase):
             # XXX Maybe on tk older than 8.4.13 it would be possible,
             # see tkinter.h.
             return
-        with test_support.EnvironmentVarGuard() as env:
+        with os_helper.EnvironmentVarGuard() as env:
             if 'DISPLAY' in os.environ:
                 del env['DISPLAY']
                 # on some platforms, deleting environment variables