test: rewrite fs {f}utimes test file

Previously this test silently swallowed some errors.

Refactored to use `common.mustCall()` & `assert()`s.

Also, this adds a couple of extra error-checking cases.

PR-URL: https://github.com/nodejs/node/pull/25656


Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Anna Henningsen <anna@addaleax.net>