[php-src] Issue #20593: Incorrect rounding in 8.4+

Issue: https://github.com/php/php-src/issues/20593
Author: 835301-cmyk

### Description

The following code:

https://3v4l.org/UMTPf
```php
<?php
$v = 190*1.15;
print("\$v = $v (190*1.15)\n");
print("round(\$v) = ".round($v)."\n");
print("round(218.5) = ".round(218.5)."\n");
```

Resulted in this output:
```
$v = 218.5 (190*1.15)
round($v) = 218
round(218.5) = 219
```
in 8.4+

But I expected this output instead:
```
$v = 218.5 (190*1.15)
round($v) = 219
round(218.5) = 219
```
It works correctly in PHP < 8.4


### PHP Version

```plain
PHP 8.4.11 (cli) (built: Aug  3 2025 07:32:21) (NTS)
Copyright (c) The PHP Group
Built by Debian
Zend Engine v4.4.11, Copyright (c) Zend Technologies
    with Zend OPcache v8.4.11, Copyright (c), by Zend Technologies
```

### Operating System

_No response_