bug #4724 Avoid ord deprecation notice in PHP 8.5 (iquito)

This PR was merged into the 3.x branch.

Discussion
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Avoid ord deprecation notice in PHP 8.5

Change the one usage of `ord()` in Twig where a multibyte character can trigger the new deprecation in PHP 8.5, which is in the `html_attr` escape functionality in EscaperRuntime, currently leading to:

```
ord(): Providing a string that is not one byte long is deprecated. Use ord($str[0]) instead"
```

This small change fixes it. There are no other usages of `ord()` in Twig which lead to this deprecation notice.

Commits
-------

4d98cce4e4 Avoid ord deprecation in PHP 8.5

src/Runtime/EscaperRuntime.php

@@ -272,7 +272,7 @@ final class EscaperRuntime implements RuntimeExtensionInterface
                      * @license   https://framework.zend.com/license/new-bsd New BSD License
                      */
                     $chr = $matches[0];
-                    $ord = \ord($chr);
+                    $ord = \ord($chr[0]);
 
                     /*
                     * The following replaces characters undefined in HTML with the