stream: fix stream.finished on Duplex

finished would incorrectly believe that a Duplex is already
closed if either the readable or writable side has completed.

Fixes: https://github.com/nodejs/node/issues/33130

PR-URL: https://github.com/nodejs/node/pull/33133


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>