xmlschema 2.5 not working for validation

[tlambert03]

not sure what happened upstream, but xmlschema 2.5 breaks tests:

    def validate_xml_with_xmlschema(
        xml: XMLSource, schema: Path | str | None = None, warn_on_schema_update: bool = True
    ) -> AnyElementTree:
        """Validate XML against an XML Schema using xmlschema."""
        from xmlschema.exceptions import XMLSchemaException

        tree = ensure_2016(xml, warn_on_schema_update=warn_on_schema_update, as_tree=True)
        xmlschema = _get_XMLSchema(schema or OME_2016_06_XSD)
        try:
            xmlschema.validate(tree)  # type: ignore[arg-type]
        except XMLSchemaException as e:
>           raise ValidationError(str(e)) from None
E           ome_types._conversion.ValidationError: failed validating <Element {http://www.openmicroscopy.org/Schemas/OME/2016-06}OME at 0x11df99a00> with XsdElement(name='OME:OME', occurs=[1, 1]):
E
E           Reason: value ('urn:lsid:loci.wisc.edu:LightSource:OWS1',) not found for XsdKey(name='OME:LightSourceIDKey') (2 times)
E
E           Schema:

it's not critical, since most people are likely using lxml anyway. but should be fixed