test: show stdout and stderr in test-cli-syntax when it fails

To help debugging the flake with the log from the CI.

PR-URL: https://github.com/nodejs/node/pull/24720
Refs: https://github.com/nodejs/node/issues/24403


Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Daniel Bevenius <daniel.bevenius@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>