Fix Pydantic issue with cached values.

[wpietri]

The Llama API is returning things that are invalid according to their Pydantic definitions, but this somehow doesn't show up as a problem until cache retrieval. Here I'm just fixing the data to match its typing. Maybe there's a better option?

[github-actions]

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[wpietri]

Per Roger, the error:

there's an issue with a meta llama SUT that just went in

E           pydantic_core._pydantic_core.ValidationError: 1 validation error for MetaLlamaModeratedResponse
E           moderation_response.results.0.flagged_categories
E             Input should be a valid list [type=list_type, input_value=None, input_type=NoneType]



FAILED plugins/validation_tests/test_object_creation.py::test_can_cache_all_sut_responses[meta-llama-4-scout-17b-16e-instruct-fp8-moderated-llama] - pydantic_core._pydantic_core.ValidationError: 1 validation error for MetaLlamaModeratedResponse
moderation_response.results.0.flagged_categories
  Input should be a valid list [type=list_type, input_value=None, input_type=NoneType]

```

[dhosterman]

I hate this, but it seems right (as far as what is under our control).