php/php-src#9325

• https://wiki.php.net/rfc/readonly_classes - Cannot create dynamic property errors should probably be thrown in msgpack_unpack() to avoid creating readonly class instances with dynamic properties
• https://wiki.php.net/rfc/deprecate_dynamic_properties - msgpack_unpack() should probably emit a deprecation notice for classes without #[AllowDynamicProperties] attributes, because in php 9.0, msgpack_unpack() on the same data would become a Error

The approach that would be used for php 8.2 unserialize() is still being discussed, but filing this to report work that would be needed to support php 8.2.