composer: update ergebnis/php-cs-fixer-config requirement (#17)

Updates the requirements on [ergebnis/php-cs-fixer-config](https://github.com/ergebnis/php-cs-fixer-config) to permit the latest version.
- [Release notes](https://github.com/ergebnis/php-cs-fixer-config/releases)
- [Changelog](https://github.com/ergebnis/php-cs-fixer-config/blob/6.56.0/CHANGELOG.md)
- [Commits](ergebnis/php-cs-fixer-config@6.55.0...6.56.0)

---
updated-dependencies:
- dependency-name: ergebnis/php-cs-fixer-config
  dependency-version: 6.56.0
  dependency-type: direct:development
...

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

composer.json

@@ -29,7 +29,7 @@
         "phpstan/phpstan": "*",
         "friendsofphp/php-cs-fixer": "^3.88",
         "ergebnis/composer-normalize": "^2.48",
-        "ergebnis/php-cs-fixer-config": "^6.55",
+        "ergebnis/php-cs-fixer-config": "^6.56",
         "phpstan/phpstan-phpunit": "2.0.7"
     },
     "config": {