test: move explanatory comment to expected location in file

Refs: https://github.com/nodejs/node/pull/30561#pullrequestreview-320172639

PR-URL: https://github.com/nodejs/node/pull/30561


Reviewed-By: Denys Otrishko <shishugi@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>