promoted property in serialized object behaves unexpected

Description

The following code:

<?php
class Foo {
    public string $bar = 'a';
    public ?string $baz = null;
    
    public function __construct(public readonly ?string $x = null) {
        
    }
}

$fooSerialized = 'O:3:"Foo":1:{s:3:"bar";s:1:"a";}a';
$fooUnserialized = unserialize($fooSerialized);

var_dump($fooUnserialized->bar); // works because exists in serialized string
var_dump($fooUnserialized->baz); // works because regular typed property, even if not existing in serialized string
var_dump($fooUnserialized->x); // Doesn't work

Resulted in this output:

string(1) "a"
NULL

Fatal error: Uncaught Error: Typed property Foo::$x must not be accessed before initialization in /in/4d6XG:18
Stack trace:
#0 {main}
  thrown in /in/4d6XG on line 18

Process exited with code 255.

But I expected this output instead:

string(1) "a"
NULL
NULL

See also https://3v4l.org/4d6XG#v8.2.6 (all versions)

PHP Version

PHP 8.2.6

Operating System

No response

Start by running the supplied PHP 8.2.6 reproducer and compare promoted readonly-property handling with the regular typed properties during unserialize(). Trace the serialization behavior involved and add or update coverage for the missing property case; done means the reproduced access yields NULL without an initialization error.