lib: refactor to use let

move variable into each for loop

PR-URL: https://github.com/nodejs/node/pull/40364


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Zijian Liu <lxxyxzj@gmail.com>
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>