[php-src] Issue #20989: Valgrind warning with ini_get + preg_match and pcre.jit=1

Issue: https://github.com/php/php-src/issues/20989
Author: chschneider

### Description

The following code:

```php
<?php

preg_match('!X!', ini_get('display_errors'));
```

When called with
```
valgrind --track-origins=yes sapi/cli/php -n -r 'preg_match("!X!", ini_get("display_errors"));'
```
resulted in this output:
```
==7649== Conditional jump or move depends on uninitialised value(s)
==7649==    at 0x523FEBF: ???
==7649==    by 0x4BA8E37: ???
==7649==    by 0x4BA8E37: ???
==7649==    by 0x4BA8E38: ???
==7649==    by 0x4CEC5DF: ???
==7649==    by 0x4BA8E37: ???
==7649==  Uninitialised value was created by a heap allocation
==7649==    at 0x4841984: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==7649==    by 0x7D0D18: __zend_malloc (zend_alloc.c:3543)
==7649==    by 0x8BC36C: zend_string_alloc (zend_string.h:167)
==7649==    by 0x8BC36C: zend_string_init (zend_string.h:189)
==7649==    by 0x8BC36C: zend_string_init_interned_permanent (zend_string.c:278)
==7649==    by 0x8BC685: zend_interned_strings_init (zend_string.c:110)
==7649==    by 0x8C867F: zend_startup (zend.c:1058)
==7649==    by 0x766B9E: php_module_startup (main.c:2253)
==7649==    by 0x47FCC4: main (php_cli.c:1329)
```

This was on x86 with openSUSE Leap 15.6, compiling the current master with `--disable-all`.

I could reproduce the warning with all PHP 8.x and older versions seem to have even more warnings which were fixed at some point.

Interestingly the warning disappears with `-d pcre.jit=0` and I assume it happens in the JIT-generated code.
Additionally when changing the preg_match pattern or ini_get-Option the warning sometimes disappears so it seems to depend on certain values/value lengths.

### PHP Version

```plain
PHP 8.6.0-dev (cli) (built: Jan 21 2026 13:29:58) (NTS)
Copyright (c) The PHP Group
Zend Engine v4.6.0-dev, Copyright (c) Zend Technologies
    with Zend OPcache v8.6.0-dev, Copyright (c), by Zend Technologies
```

### Operating System

openSUSE Leap 15.6