Generating labels of validate.OneOf(labels=[..]) in the json schema

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Hi,

I have the following field in marshmallow:

```python
the_field = fields.Integer(validate=[validate.OneOf([1, 2, 3], labels=['one', 'two', 'three'])])
```

And the resulting json:
```
"the_field": {
"type": "integer",
"enum": [
1,
2,
3
]
}
```

Is there a way to also print the labels `['one', 'two', 'three']` in the json ?

No file or test is named in the issue. Start by locating the schema-generation path that handles marshmallow validate.OneOf and compare its current enum output with the requested labels; done means the generated JSON schema represents the labels as intended and existing behavior remains covered.

Written by the indexing model from the issue text.