fake.Json fails with snowfakery_version: 3

[rrutum]

- var: snowfakery_locale
  value: en_US
- snowfakery_version: 3
- object: SomeObject
  fields:
    formula_field_example: ${{fake.Json(data_columns={'Spec':'@1.0.1', 'ID':'pyint',
      'Details':{'Name':'name', 'Address':'address'}}, num_rows=2)}}

output:

snowfakery.data_gen_exceptions.DataGenValueError: Field 'formula_field_example' generated unexpected object: [{'Spec': '1.0.1', 'ID': 5730, 'Details': {'Name': 'Mrs. Samantha Brandt DVM', 'Address': '60884 Kathy Motorway\nLake Bernard, AZ 76551'}}, {'Spec': '1.0.1', 'ID': 9314, 'Details': {'Name': 'John Fowler', 'Address': 'PSC 9160, Box 4669\nAPO AE 08490'}}] <class 'list'>
 near /Users/rrutumlavana/Documents/repos/data-synthesizer-definitions/discoball/discoblueaerospike/snowfakery.yaml:4

This works with snowfakery_version 2

[rrutum]

#1097 this PR solves the issue