Update dependency phpunit/phpunit to v9.6.18

Author: renovate[bot]

composer.json

@@ -26,7 +26,7 @@
         "doctrine/annotations": "^1.6"
     },
     "require-dev": {
-        "phpunit/phpunit": "7.5.20|9.5.0",
+        "phpunit/phpunit": "9.6.18",
         "sunrise/coding-standard": "1.0.0",
         "sunrise/http-factory": "1.1.0",
         "sunrise/http-router": "^2.11",