[FIX] model_generic.mustache

to_json() formatting

Author: padznich

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

@@ -168,7 +168,7 @@ class {{classname}}({{#parent}}{{{.}}}{{/parent}}{{^parent}}BaseModel{{/parent}}
 
     def to_json(self) -> str:
         """Returns the JSON representation of the actual instance"""
-        return self.model_dump_json(by_alias=True, exclude_none=True)
+        return json.dumps(self.model_dump(by_alias=True, exclude_none=True))
 
     def to_dict(self) -> Dict[str, Any]:
         """Returns the dict representation of the actual instance"""