util: add coverage for util.inspect.colors alias setter

Add test to confirm that the setter for aliases in `util.inspect.colors`
keeps the alias reference-equal to the target value.

Refs: https://coverage.nodejs.org/coverage-5b0308cd823a5110/lib/internal/util/inspect.js.html#L357
Refs: https://codecov.io/gh/nodejs/node/src/5b0308cd823a511098dadf9ddd5a35e3a9dbb424/lib/internal/util/inspect.js#L357

PR-URL: https://github.com/nodejs/node/pull/31743


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>