Log Message:
py-xmlschema: updated to 2.2.1

`v2.2.1`_ (2023-02-11)
* Fix mixed content extension without explicit mixed attribute

`v2.2.0`_ (2023-02-06)
* Refine string serialization of XML resources and data elements
* Switch to use elementpath v4
* Fix sequence_type property for XSD types
* Remove *XsdElement.get_attribute()*: unused and doesn't work as expected