Fix TestMetadataJsonFormat test failures

[scotts]

These are failing on CUDA, but not on ROCm:

1. TestMetadataJsonFormat::test_kernel_metadata_field_types
2. TestMetadataJsonFormat::test_kernel_metadata_has_expected_fields
3. TestMetadataJsonFormat::test_metadata_json_is_valid_json_fragment
4. TestMetadataJsonFormat::test_metadata_json_key_value_format

See: https://github.com/pytorch/kineto/actions/runs/27250266182/job/80473089883?pr=1428