test: remove string literal from assertion

Remove string literal from `assert.strictEqual()` call `message`
parameter and make it a comment above the assertion instead.

Backport-PR-URL: https://github.com/nodejs/node/pull/22888
PR-URL: https://github.com/nodejs/node/pull/22849


Reviewed-By: Teddy Katz <teddy.katz@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>