PHP 8.4: compile error

[mokraemer]

The new corrected type definitions in subproject xml was not correctly mapped to this project:
Type of Sabre\DAV\Xml\Service::$elementMap must be array (as in class Sabre\Xml\Service)

In addition, I suggest doing this in the constructor, instead of replacing a parent property, which will also raise deprecation warnings.

[mokraemer]

• Declaration of Sabre\DAV\Xml\Element\Response::xmlSerialize(Sabre\Xml\Writer $writer) must be compatible with Sabre\Xml\XmlSerializable::xmlSerialize(Sabre\Xml\Writer $writer): void
• Sabre\DAV\Xml\Property\GetLastModified::xmlSerialize(Sabre\Xml\Writer $writer) must be compatible with Sabre\Xml\XmlSerializable::xmlSerialize(Sabre\Xml\Writer $writer): void
• Sabre\DAV\Xml\Property\LockDiscovery::xmlSerialize(Sabre\Xml\Writer $writer) must be compatible with Sabre\Xml\XmlSerializable::xmlSerialize(Sabre\Xml\Writer $writer): void