bug symfony#58195 [Process] Fix the removal of host-specific configuration when managing the ini settings in PhpSubprocess (M-arcus)

This PR was submitted for the 7.1 branch but it was merged into the 6.4 branch instead.

Discussion
----------

[Process] Fix the removal of host-specific configuration when managing the ini settings in `PhpSubprocess`

| Q             | A
| ------------- | ---
| Branch?       | 6.4
| Bug fix?      | yes
| New feature?  | no
| Deprecations? | no
| Issues        |
| License       | MIT

`preg_match` can return the offset needed for `substr` in the next line, but without the flag it doesn't put the offset of the capturing group into `$matches[0][1]`

With the example php.ini the code breaks on execution

```ini
opcache.validate_timestamps = 0
[HOST=my.test.host]
opcache.validate_timestamps = 1
```

Commits
-------

1ef6bf7 PhpSubprocess: Add flag PREG_OFFSET_CAPTURE to preg_match to identify the offset

Author: nicolas-grekas

src/Symfony/Component/Process/PhpSubprocess.php

@@ -106,7 +106,7 @@ private function writeTmpIni(array $iniFiles, string $tmpDir): string
                 throw new RuntimeException('Unable to read ini: '.$file);
             }
             // Check and remove directives after HOST and PATH sections
-            if (preg_match('/^\s*\[(?:PATH|HOST)\s*=/mi', $data, $matches)) {
+            if (preg_match('/^\s*\[(?:PATH|HOST)\s*=/mi', $data, $matches, \PREG_OFFSET_CAPTURE)) {
                 $data = substr($data, 0, $matches[0][1]);
             }