test: change Fixes: to Refs:

Tests don't fix things generally, so use "Refs:" to refer people to
GitHub issues.

PR-URL: https://github.com/nodejs/node/pull/34568


Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>