[php-src] Issue #21605: Missing addref for Countable::count()

Issue: https://github.com/php/php-src/issues/21605
Author: iluuu1994

### Description

### Description

The following code:

```php
<?php

class C implements Countable {
    public function count(): int {
        global $c;
        $c = null;
        var_dump($this);
        return 42;
    }
}

$c = new C;
var_dump(count($c));
```

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_