Look for modules in test_alias_modules_exist, not files

Author: hroncok

Lib/test/test_codecs.py

@@ -3111,11 +3111,9 @@ def test_aliases(self):
     def test_alias_modules_exist(self):
         encodings_dir = os.path.dirname(encodings.__file__)
         for value in encodings.aliases.aliases.values():
-            codec_file = os.path.join(encodings_dir, value + ".py")
-            pyc_file = codec_file + "c"
-            self.assertTrue(os.path.isfile(codec_file)
-                            or os.path.isfile(pyc_file),
-                            "Codec file not found: " + codec_file)
+            codec_mod = f"encodings.{value}"
+            self.assertIsNotNone(importlib.util.find_spec(codec_mod),
+                                 "Codec module not found: " + codec_mod)
 
     def test_quopri_stateless(self):
         # Should encode with quotetabs=True