Fix error message regex

Author: msimacek

graalpython/com.oracle.graal.python.test/src/tests/test_codecs.py

@@ -877,7 +877,7 @@ def test_encode(self):
 
 class UTF32Test(unittest.TestCase):
     def test_utf32_surrogate_error(self):
-        with self.assertRaisesRegex(UnicodeDecodeError, "'utf_32' codec can't decode bytes in position 4-7"):
+        with self.assertRaisesRegex(UnicodeDecodeError, "codec can't decode bytes in position 4-7"):
             b'a\x00\x00\x00\x00\xd8\x00\x00z\x00\x00\x00'.decode('utf-32')