Issue #16414: Fix test_os on Windows, don't test os.listdir() with undecodable

Issue #16414: Fix test_os on Windows, don't test os.listdir() with undecodable

With the ANSI code page 932, os.listdir(b'\xe7') return an empty list (instead
of failing), whereas os.listdir(b'\xff') raises a FileNotFoundError.

It looks like a Windows bug: b'\xe7' directory does not exist,
FindFirstFileA(b'\xe7') fails with ERROR_FILE_NOT_FOUND (2), instead of
ERROR_PATH_NOT_FOUND (3).