[php-src] Issue #22817: The array_keys function casts the keys

Issue: https://github.com/php/php-src/issues/22817
Author: tomasnajman

### Description

When using the array_keys function, a cast from string to int occurs. The function should not change the value if the text value of the key looks like a number.

The following code:

```php
<?php
$array = ['first' => '1', '2' => '2'];
$keys = \array_keys($array);
echo \json_encode($keys);
```

Resulted in this output:
```
["first",2]
```

But I expected this output instead:
```
["first","2"]
```


### PHP Version

```plain
PHP 8.4.23 (cli) (built: Jul  1 2026 04:47:16) (NTS Visual C++ 2022 x64)
Copyright (c) The PHP Group
Built by The PHP Group
Zend Engine v4.4.23, Copyright (c) Zend Technologies
    with the ionCube PHP Loader v15.5.0, Copyright (c) 2002-2026, by ionCube Ltd.
```

### Operating System

Windows 11