[Bug]: mypy error: Name "JSON" is not defined [name-defined]

### Describe the bug

I used autorest: 3.9.5, generator: @autorest/python@6.28.4 to generate search. Here is a mypy error in _models_py3.py.

Name "JSON" is not defined [name-defined]

Seems like we missed we miss JSON = MutableMapping[str, Any] in the code gen?

### Reproduction

In order to repro, you can try to generate code using https://github.com/Azure/azure-rest-api-specs/tree/main/specification/search/data-plane/Azure.Search/preview/2025-03-01-preview

### Checklist

- [x] Follow our [Code of Conduct](https://github.com/microsoft/typespec/blob/main/CODE_OF_CONDUCT.md)
- [x] Check that there isn't already an issue that request the same bug to avoid creating a duplicate.
- [x] Check that this is a concrete bug. For Q&A open a [GitHub Discussion](https://github.com/Microsoft/typespec/discussions).
- [x] The provided reproduction is a [minimal reproducible example](https://stackoverflow.com/help/minimal-reproducible-example) of the bug.