Update friendsofphp/php-cs-fixer requirement from 3.16.0 to 3.20.0

Updates the requirements on [friendsofphp/php-cs-fixer](https://github.com/PHP-CS-Fixer/PHP-CS-Fixer) to permit the latest version.
- [Release notes](https://github.com/PHP-CS-Fixer/PHP-CS-Fixer/releases)
- [Changelog](https://github.com/PHP-CS-Fixer/PHP-CS-Fixer/blob/master/CHANGELOG.md)
- [Commits](PHP-CS-Fixer/PHP-CS-Fixer@v3.16.0...v3.20.0)

---
updated-dependencies:
- dependency-name: friendsofphp/php-cs-fixer
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <support@github.com>

composer.json

@@ -39,7 +39,7 @@
     "require-dev": {
         "phpunit/phpunit": "^9.5.10",
         "phpstan/phpstan": "1.10.15",
-        "friendsofphp/php-cs-fixer": "3.16.0",
+        "friendsofphp/php-cs-fixer": "3.20.0",
         "maglnet/composer-require-checker": "^3.0.0",
         "phpro/grumphp-shim": "^1.5.0"
     },