[php-src] Issue #21639: Volatile arguments in frameless calls

Issue: https://github.com/php/php-src/issues/21639
Author: iluuu1994

### Description

```php
<?php

class C {
    public function __toString(): string {
        global $arr;
        $arr = null;
        return "C";
    }
}

$arr = [new C, 42];
implode(", ", $arr);
```

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

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

Originally reported by @cnwangjihe.

### PHP Version

```plain
PHP 8.4+
```

### Operating System

_No response_