[php-src] Issue #21603: Missing addref for __unset

Issue: https://github.com/php/php-src/issues/21603
Author: iluuu1994

### Description

The following code:

```php
<?php

class C {
    public function __unset($name) {
        global $c;
        $c = null;
        var_dump($this);
    }
}

$c = new C;
unset($c->prop);
```

Resulted in this output:
```
Segfault
```

But I expected this output instead:
```
```

Originally reported by @cnwangjihe.

### PHP Version

```plain
PHP 8.2+
```

### Operating System

_No response_