test: add check for root user

Currently this test fails if run as the root user:
Mismatched innerFn function calls. Expected exactly 62, actual 42.

The motivation for this is that when building node in a docker
container it is convenient to be able to build as root.

PR-URL: https://github.com/nodejs/node/pull/19850


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>