doc: fs.write is not longer coercing strings

PR-URL: https://github.com/nodejs/node/pull/31030


Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Yongsheng Zhang <zyszys98@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>