test: fix test-dns-idna2008.js

The test should pass if ESERVFAIL is the result.

Refs: https://github.com/nodejs/node/issues/25870#issuecomment-471024667

PR-URL: https://github.com/nodejs/node/pull/27208


Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>