Tests: add package description metadata retrieval for Python 3.9 and earlier

[jayaddison]

Enables the unit test added in #1162 to run on all of the versions of Python supported by the library.

[jknndy]

What's the appropriate timeline for dropping support of outdated python versions? Is it project-preference or is there a standard recommendation?

[jayaddison]

What's the appropriate timeline for dropping support of outdated python versions? Is it project-preference or is there a standard recommendation?

It is project preference, yep. That said, some standard practices, such as Scientific Python's SPEC-0, do exist.

Because this library doesn't have many or complex dependencies, I think it generally makes sense to support a fairly wide version range.

Dropping Python versions when they're no longer supported by upstream Python (see the Python devguide version reference) can make sense to encourage people to upgrade, and to allow us to gradually opt-in to more recent language features (pyupgrade is one way to check for some commonly-recommended ideas).

[jayaddison]

Thank you for the code review @jknndy!