Upgrade PHPUnit to v9.0

Author: lcobucci

composer.json

@@ -28,7 +28,7 @@
         "phpstan/phpstan-deprecation-rules": "^0.12",
         "phpstan/phpstan-phpunit": "^0.12",
         "phpstan/phpstan-strict-rules": "^0.12",
-        "phpunit/phpunit": "^8.2",
+        "phpunit/phpunit": "^9.0",
         "squizlabs/php_codesniffer": "^3.5"
     },
     "autoload": {