test: use .test domain for not found address

While it is extremely unlikely that `.fhqwhgads` will become a valid
domain, we should, where possible, use one of the reserved domains for
testing.

Refs: https://tools.ietf.org/html/rfc2606

PR-URL: https://github.com/nodejs/node/pull/38286
Refs: https://github.com/nodejs/node/pull/38282


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>