Don't use sebTest() in tests for issue #5815.

Lib/test/test_locale.py

@@ -371,8 +371,7 @@ class NormalizeTest(unittest.TestCase):
 
     def test_locale_alias(self):
         for localename, alias in locale.locale_alias.items():
-            with self.subTest(locale=(localename, alias)):
-                self.check(localename, alias)
+            self.check(localename, alias)
 
     def test_empty(self):
         self.check('', '')