test: use fixtures in test-https-set-timeout-server

Task to replace the common.fixturesDir with the usage
of the common.fixtures module. At Node.js Interactive.
First PR to Node.js. Yay!

PR-URL: https://github.com/nodejs/node/pull/15886


Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: James M Snell <jasnell@gmail.com>