test: increase coverage for assert/calltracker

1. test calls fn parameter is number
Refs: https://coverage.nodejs.org/coverage-51b43675067fafaa/lib/internal/assert/calltracker.js.html#L30

2. test calls fn parameter is undefined
Refs: https://coverage.nodejs.org/coverage-51b43675067fafaa/lib/internal/assert/calltracker.js.html#L33

PR-URL: https://github.com/nodejs/node/pull/36728


Reviewed-By: Rich Trott <rtrott@gmail.com>