test: use common.fixtures module for file path

PR-URL: https://github.com/nodejs/node/pull/16017


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>