test: check null proto-of-proto in util.inspect()

Add a test to check util.inspect()'s handling of a null
prototype-of-an-iterable-prototype. This covers a previously uncovered
code branch.

Refs: https://coverage.nodejs.org/coverage-0fd121e00c9d5987/lib/internal/util/inspect.js.html#L597

PR-URL: https://github.com/nodejs/node/pull/36399


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: Daijiro Wachi <daijiro.wachi@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>