use different codec alias names in test code than in optimiser code to check...

use different codec alias names in test code than in optimiser code to check that the alias name resolution works

tests/run/bytesmethods.pyx

@@ -162,7 +162,7 @@ def bytes_decode_utf16(bytes s):
     >>> print(bytes_decode_utf16(s))
     abc
     """
-    return s.decode('UTF-16')
+    return s.decode('utf16')
 
 
 @cython.test_assert_path_exists(
@@ -176,7 +176,7 @@ def bytes_decode_utf16_le(bytes s):
     >>> print(bytes_decode_utf16_le(s))
     abc
     """
-    return s.decode('UTF-16LE')
+    return s.decode('utf_16_le')
 
 
 @cython.test_assert_path_exists(
@@ -190,7 +190,7 @@ def bytes_decode_utf16_be(bytes s):
     >>> print(bytes_decode_utf16_be(s))
     abc
     """
-    return s.decode('UTF-16BE')
+    return s.decode('utf_16_be')
 
 
 @cython.test_assert_path_exists(