AIS marking emits invalid string on Python 3

[gtback]

This is an example of an invalid XML fragment emitted by the AIS marking binding.

<AIS:AISMarkingStructure
        xmlns:AIS="http://www.us-cert.gov/STIXMarkingStructure#AISConsentMarking-2"
        xmlns:marking="http://data-marking.mitre.org/Marking-1"
        xmlns:example="http://example.com"
        xmlns:xlink="http://www.w3.org/1999/xlink"
        xmlns:ds="http://www.w3.org/2000/09/xmldsig#"
        xmlns:xs="http://www.w3.org/2001/XMLSchema"
        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:type=b'"AIS:AISMarkingStructure"'>
    <AIS:Is_Proprietary CISA_Proprietary="true">
        <AIS:AISConsent consent="EVERYONE"/>
        <AIS:TLPMarking color="AMBER"/>
    </AIS:Is_Proprietary>
</AIS:AISMarkingStructure>

Note the b'"AIS:AISMarkingStructure"' in the middle. Looks like Unicode strings and byte strings are getting improperly mixed.