tty: enable buffering

HWM was set to 0 which would cause e.g. stdout.write(...) to
always return false.

Refs: https://github.com/nodejs/node/pull/39246

PR-URL: https://github.com/nodejs/node/pull/39253


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>