Update dependency phpunit/phpunit to v9.6.7

Author: renovate[bot]

composer.json

@@ -33,7 +33,7 @@
         "php": "^7.1|^8.0"
     },
     "require-dev": {
-        "phpunit/phpunit": "7.5.20|9.5.0",
+        "phpunit/phpunit": "9.6.7",
         "sunrise/coding-standard": "1.0.0"
     },
     "autoload": {