Reverting last commit to use run_with_locale only

`run_with_locales` is a decorator-only but would run all specified locales,
skipping those that cannot be found. Instead, we use `run_with_locale`
which is a context manager *and* a decorator to speed-up tests.

Author: picnixz

Lib/test/test_ctypes/test_dlerror.py

@@ -123,7 +123,7 @@ class TestLocalization(unittest.TestCase):
 
     @staticmethod
     def configure_locales(func):
-        return test.support.run_with_locales(
+        return test.support.run_with_locale(
             'LC_ALL',
             'fr_FR.iso88591', 'ja_JP.sjis', 'zh_CN.gbk',
             'fr_FR.utf8', 'en_US.utf8',

Lib/test/test_dbm_gnu.py

@@ -206,7 +206,7 @@ def test_clear(self):
                 self.assertNotIn(k, db)
             self.assertEqual(len(db), 0)
 
-    @support.run_with_locales(
+    @support.run_with_locale(
         'LC_ALL',
         'fr_FR.iso88591', 'ja_JP.sjis', 'zh_CN.gbk',
         'fr_FR.utf8', 'en_US.utf8',