test: mark test-cli-syntax as flaky/unreliable

Refs: https://github.com/nodejs/node/issues/24403

PR-URL: https://github.com/nodejs/node/pull/24957


Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Daijiro Wachi <daijiro.wachi@gmail.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>