Validation bypass of extra data keys in JSON model validation

Summary

When validating JSON data into a model allowing extra data, the keys of extra data aren't validated against the key type annotated on __pydantic_extra__, resulting in extra data not matching the declared type. This is the case if you define __pydantic_extra__ as e.g. dict[Annotated[str, Field(pattern=r'^x_')], int].

Details

The validate_json_by_iteration() method (in pydantic-core/src/validators/model_fields.rs), used to validate JSON data into models, only validates the values of extra data, and stores the keys as is (L605-L623):

ExtraBehavior::Allow => {
    // the key is stored as is, without being validated:
    let py_key: Bound<'_, PyString> = new_py_string(py, key, state.());
      (validator) = &.extras_validator {
         validator.(py, value, state) {
            (value) => {
                model_extra_dict.(&py_key, value)?;
                fields_set.(py_key)?;
            }
            
        }
    }
    
}