composer(deps): update symfony/string requirement in /packages/guides

Updates the requirements on [symfony/string](https://github.com/symfony/string) to permit the latest version.
- [Release notes](https://github.com/symfony/string/releases)
- [Changelog](https://github.com/symfony/string/blob/7.1/CHANGELOG.md)
- [Commits](symfony/string@v6.4.7...v6.4.8)

---
updated-dependencies:
- dependency-name: symfony/string
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

packages/guides/composer.json

@@ -31,7 +31,7 @@
         "phpdocumentor/flyfinder": "^1.1",
         "psr/event-dispatcher": "^1.0",
         "symfony/clock": "^6.4.7",
-        "symfony/string": "^6.4.7",
+        "symfony/string": "^6.4.8",
         "symfony/translation-contracts": "^3.5.0",
         "symfony/http-client": "^6.4.7",
         "twig/twig": "~2.15 || ^3.0",