test: replace common.fixturesDir

In test/parallel/test-tls-junk-closes-server.js, replaced
common.fixtruesDir with usage of the common.fixtrues module.

PR-URL: https://github.com/nodejs/node/pull/15834


Reviewed-By: Ryan Graham <r.m.graham@gmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>