Julia list assignment has unused "mut"
Position 0 of format string became unused in https://github.com/adsharma/py2many/commit/989693b403a0a1c036b1568549a41f4de8c7499a#diff-2bf4f7a95e4998fbc465c316438c3919aa0797650c53a34690d635832b5d96dcR477 .  The logic for choosing mutability is wrong, resulting in invalid code if `{0}` is added.