bpo-40275: Use new test.support helper submodules in tests (GH-21317)

diff --git a/Lib/test/test_set.py b/Lib/test/test_set.py
index 68d4942..e45f018 100644
--- a/Lib/test/test_set.py
+++ b/Lib/test/test_set.py
@@ -1,5 +1,6 @@
 import unittest
 from test import support
+from test.support import warnings_helper
 import gc
 import weakref
 import operator
@@ -953,7 +954,7 @@
 
 class TestBasicOpsMixedStringBytes(TestBasicOps, unittest.TestCase):
     def setUp(self):
-        self._warning_filters = support.check_warnings()
+        self._warning_filters = warnings_helper.check_warnings()
         self._warning_filters.__enter__()
         warnings.simplefilter('ignore', BytesWarning)
         self.case   = "string and bytes set"