Clean up warnings filter use in test_global by no longer having it be a

module-level manipulation of the filter.

Lib/test/test_global.py

 """Verify that warnings are issued for global statements following use."""
 
-from test.support import run_unittest, check_syntax_error
+from test.support import run_unittest, check_syntax_error, check_warnings
 import unittest
 
 import warnings
-warnings.filterwarnings("error", module="<test string>")
+
 
 class GlobalTests(unittest.TestCase):
 
+    def setUp(self):
+        self._warnings_manager = check_warnings()
+        self._warnings_manager.__enter__()
+        warnings.filterwarnings("error", module="<test string>")
+
+    def tearDown(self):
+        self._warnings_manager.__exit__(None, None, None)
+
+
     def test1(self):
         prog_text_1 = """\
 def wrong1():