Adding a sort order validation test

[rambleraptor]

Rationale for this change

This test shows the error that iceberg-rest-fixture is throwing for a Sort Order that references a field that doesn't exist.

Are these changes tested?

Are there any user-facing changes?

[Fokko]

What are we testing here from a PyIceberg perspective? I think this should be part of the Rest Fixtures tests?

[rambleraptor]

I've moved this over to a draft.

I built this test mostly as a POC for https://lists.apache.org/thread/2h33jt9flnxctjtwsl3od9yxxbhmcvov. Writing it in Python makes it very obvious what JSON is being returned.

[Fokko]

Ah, I see. That makes sense. Thanks for the context 👍

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[github-actions]

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