guard ToXmlGenerator cast in serializeWithType()/_serializeObjectId() for convertValue()

[Sahana2524]

ClassCastException from XmlMapper.valueToTree() / convertValue() on any @JsonTypeInfo(include = As.PROPERTY) bean (the default inclusion):

java.lang.ClassCastException: class tools.jackson.databind.node.TreeBuildingGenerator
    cannot be cast to class tools.jackson.dataformat.xml.ser.ToXmlGenerator

serializeWithType() and _serializeObjectId() cast the generator to ToXmlGenerator to flag the type id as an attribute, but those two conversion entry points serialize into a TokenBuffer / tree generator rather than a ToXmlGenerator. The sibling methods _serializeProperties() and _serializePropertiesFiltered() in the same class already skip the XML-specific handling with an instanceof ToXmlGenerator guard (comment: "During 'convertValue()', need to skip"); these two type-id paths were the only ones missing it, so I added the same guard to both.

Real XML serialization is unchanged: the type id is still written as an attribute. Added a small regression test covering valueToTree, convertValue, and the unchanged XML output.

[github-actions]

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