n-api: fix object test

Passing a pointer to a static integer is sufficient for the test.

PR-URL: https://github.com/nodejs/node/pull/19039


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: Hitesh Kanwathirtha <hiteshk@microsoft.com>