test(gc): simplify logic to assert gc review due dates (#747)

Related to #747 (closed)

🌱 Context

See #747 (closed) for full context on why we are making this change.

In summary, we want to be able to assert the time range of a variable (i.e GC review delay) falls within an acceptable bounds in our tests without duplicating the checking logic across multiple tests. To do this we have decided to implement the following refactor in this MR:

• Define 2 new constants to be shared across test cases
• Create a helper function to assert the necessary GC delay range requirement (without duplicating the test code)