Allow PHPUnit v13 (#171)

https://claude.ai/code/session_01LRy8BQjokyWrEaor5VtfYF

Co-authored-by: Claude <noreply@anthropic.com>

Author: simPod

composer.json

@@ -15,7 +15,7 @@
     "require": {
         "php": "^8.1",
         "matthiasnoback/symfony-config-test": "^5.0 || ^6.0",
-        "phpunit/phpunit": "^10.5.11 || ^11.5 || ^12.0",
+        "phpunit/phpunit": "^10.5.11 || ^11.5 || ^12.0 || ^13.0",
         "symfony/dependency-injection": "^5.4 || ^6.4 || ^7.0 || ^8.0",
         "symfony/deprecation-contracts": "^2.5 || ^3.0",
         "symfony/config": "^5.4 || ^6.4 || ^7.0 || ^8.0",