os: fix memory leak in `userInfo()`

This previously leaked memory in the ‘success’ case.

PR-URL: https://github.com/nodejs/node/pull/23893


Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: James M Snell <jasnell@gmail.com>