doc: fix lint errors in packages.md

Code samples that use CJS-only syntax need to use the cjs markdown
identifiers.

PR-URL: https://github.com/nodejs/node/pull/39792


Reviewed-By: Richard Lau <rlau@redhat.com>
Reviewed-By: Myles Borins <myles.borins@gmail.com>
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: Robert Nagy <ronagy@icloud.com>