Add Subclass Tests

[coneybeare]

In my project, I came across an issue that I cannot reproduce in the tests, so it must be a difference in the way I load the rails project code, or perhaps in the switch to Zeitwerk loader. None-the-less, here are two tests that show superclass handling is working correctly for values.

I could not reproduce on the latest version of ruby (3.3.4 at the time of this PR)

[dangerpr-bot]

	1 Warning
⚠️	Unless you're refactoring existing code or improving documentation, please update CHANGELOG.md.

Here's an example of a CHANGELOG.md entry:

* [#50](https://github.com/dblock/ruby-enum/pull/50): Add subclass tests - [@coneybeare](https://github.com/coneybeare).

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[dblock]

Interesting! I'd love to know what's going on in your project.

Care to update rubocop to get a 🍏 build? I'd like to merge the tests.