allow lower phpunit

Author: Oliver Kossin

composer.json

@@ -27,7 +27,7 @@
         "phpstan/phpstan-doctrine": "^1.0",
         "phpstan/phpstan-phpunit": "^1.0",
         "phpstan/phpstan-symfony": "^1.0",
-        "phpunit/phpunit": "^9.6",
+        "phpunit/phpunit": "^8.0 ||^9.6",
         "symfony/browser-kit": "^5.4 || ^6.0 || ^7.0",
         "symfony/dotenv": "^5.4 || ^6.0 || ^7.0",
         "symfony/form": "^5.4 || ^6.0 || ^7.0",