src: exit explicitly after printing V8 help

V8 will not exit the process after handling --help anymore:
https://chromium-review.googlesource.com/c/v8/v8/+/2276276

As a drive-by fix, correctly return in the `print_bash_completion`
case as well.

Refs: https://github.com/nodejs/node/pull/34135


Co-authored-by: Ulan Degenbaev <ulan@chromium.org>

PR-URL: https://github.com/nodejs/node/pull/34136


Reviewed-By: Shelley Vohr <codebytere@gmail.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Daniel Bevenius <daniel.bevenius@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>