update test_getopt.py from cpython 3.11.2

Author: jinnarajin

Lib/test/test_getopt.py

@@ -11,14 +11,10 @@
 
 class GetoptTests(unittest.TestCase):
     def setUp(self):
-        self.env = EnvironmentVarGuard()
+        self.env = self.enterContext(EnvironmentVarGuard())
         if "POSIXLY_CORRECT" in self.env:
             del self.env["POSIXLY_CORRECT"]
 
-    def tearDown(self):
-        self.env.__exit__()
-        del self.env
-
     def assertError(self, *args, **kwargs):
         self.assertRaises(getopt.GetoptError, *args, **kwargs)