test: use common.fixtures.path()

PR-URL: https://github.com/nodejs/node/pull/16112


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Stephen Belanger <admin@stephenbelanger.com>