[python] Update Markdown files for Models with fixed Python print() syntax (#17993)

* Update Markdown file with fixed Python example

* ./bin/generate-samples.sh ./bin/configs/*.yaml

samples/openapi3/client/petstore/python-aiohttp/docs/Client.md

@@ -17,7 +17,7 @@ json = "{}"
 # create an instance of Client from a JSON string
 client_instance = Client.from_json(json)
 # print the JSON string representation of the object
-print Client.to_json()
+print(Client.to_json())
 
 # convert the object into a dict
 client_dict = client_instance.to_dict()