buffer: fix concat error message

The list argument may only be of type array, not of any other type
as it actually suggests.

PR-URL: https://github.com/nodejs/node/pull/27050


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Yongsheng Zhang <zyszys98@gmail.com>