test: simplify date inspection tests

The code duplicated a lot of logic that was already abstracted. Use
the abstraction instead to remove code overhead.

PR-URL: https://github.com/nodejs/node/pull/26922


Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Anto Aravinth <anto.aravinth.cse@gmail.com>