[BUG][Python] model_to_dict fails when x is a dictionary in model_utils.py

Created by: code-lucidal58

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Have you provided a full/minimal spec to reproduce the issue?
Have you validated the input using an OpenAPI validator (example)?
Have you tested with the latest master to confirm the issue still exists?
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Description

            if isinstance(value, list):
                if not value or isinstance(value[0], PRIMITIVE_TYPES):
                    # empty list or primitive types
                    result[attr] = value
                elif isinstance(value[0], ModelSimple):
                    result[attr] = [x.value for x in value]
                else:
                    result[attr] = [model_to_dict(x, serialize=serialize) for x in value]

In the else part, if x is a dictionary, meaning value is a list of dictionaries, model_to_dict fails. Because x is not a valid and model_to_dict, assuming it to be a model, tries to access the _composed_schemas.

openapi-generator version

master build and released v5.0.1

Suggest a fix

Check if x is a model by checking if it has the _data_store property. This was the approach before the 5th Jan commit to this file. https://github.com/OpenAPITools/openapi-generator/pull/8387