Update dependency phpunit/phpunit to v9

Author: renovate[bot]

composer.json

@@ -33,7 +33,7 @@
         "phpstan/phpstan-mockery": "^1.0.0",
         "phpstan/phpstan-phpunit": "^1.0.0",
         "phpstan/phpstan-strict-rules": "^1.0.0",
-        "phpunit/phpunit": "^8.0",
+        "phpunit/phpunit": "^9.0",
         "roave/security-advisories": "dev-master",
         "slevomat/coding-standard": "dev-master as 5.0.4",
         "thecodingmachine/phpstan-safe-rule": "^1.0.0"