[python] change Private attr to Class vars (#16687)

* [python] fix TypeError

Signed-off-by: ふぁ <yuki@yuki0311.com>

* [python] update Private model attributes to Class vars

Signed-off-by: ふぁ <yuki@yuki0311.com>

* [python] rename the List of test cases to ListClass

Signed-off-by: ふぁ <yuki@yuki0311.com>

* [python] update samples

Signed-off-by: ふぁ <yuki@yuki0311.com>

* [python] rename the List of v1 test cases to ListClass

Signed-off-by: ふぁ <yuki@yuki0311.com>

* [python] rename the List of v1-aiohttp test cases to ListClass

Signed-off-by: ふぁ <yuki@yuki0311.com>

* update samples

---------

Signed-off-by: ふぁ <yuki@yuki0311.com>
Co-authored-by: William Cheng <wing328hk@gmail.com>

samples/openapi3/client/petstore/python-pydantic-v1/.openapi-generator/FILES

@@ -49,7 +49,7 @@ docs/HasOnlyReadOnly.md
 docs/HealthCheckResult.md
 docs/InnerDictWithProperty.md
 docs/IntOrString.md
-docs/List.md
+docs/ListClass.md
 docs/MapOfArrayOfModel.md
 docs/MapTest.md
 docs/MixedPropertiesAndAdditionalPropertiesClass.md
@@ -146,7 +146,7 @@ petstore_api/models/has_only_read_only.py
 petstore_api/models/health_check_result.py
 petstore_api/models/inner_dict_with_property.py
 petstore_api/models/int_or_string.py
-petstore_api/models/list.py
+petstore_api/models/list_class.py
 petstore_api/models/map_of_array_of_model.py
 petstore_api/models/map_test.py
 petstore_api/models/mixed_properties_and_additional_properties_class.py