Fix Python .to_json to use Pydantic .model_dump_json

This fixes an issue when exporting models with UUID fields

Author: EspenHa

modules/openapi-generator/src/main/resources/python/model_generic.mustache

@@ -127,8 +127,7 @@ class {{classname}}({{#parent}}{{{.}}}{{/parent}}{{^parent}}BaseModel{{/parent}}
 
     def to_json(self) -> str:
         """Returns the JSON representation of the model using alias"""
-        # TODO: pydantic v2: use .model_dump_json(by_alias=True, exclude_unset=True) instead
-        return json.dumps(self.to_dict())
+        return self.model_dump_json(by_alias=True, exclude_unset=True)
 
     @classmethod
     def from_json(cls, json_str: str) -> Optional[{{^hasChildren}}Self{{/hasChildren}}{{#hasChildren}}{{#discriminator}}Union[{{#mappedModels}}{{{modelName}}}{{^-last}}, {{/-last}}{{/mappedModels}}]{{/discriminator}}{{^discriminator}}Self{{/discriminator}}{{/hasChildren}}]: