test: relax expectations in test-icu-transcode

Chromium's ICU considers "latin1" and "ascii" to mean Windows-1252,
which is consistent with
[WHATWG spec](https://encoding.spec.whatwg.org/#names-and-labels). If
linked against Chromium's ICU, Node.js therefore fails
`test/parallel/test-icu-transcode`.

PR-URL: https://github.com/nodejs/node/pull/25866
Refs: https://github.com/nodejs/node/issues/25851


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Tiancheng "Timothy" Gu <timothygu99@gmail.com>