Update dependency phpunit/phpunit to v9.6.11

Author: renovate[bot]

composer.json

@@ -28,7 +28,7 @@
     "psr/log": "^1.1"
   },
   "require-dev": {
-    "phpunit/phpunit": "9.5.9",
+    "phpunit/phpunit": "9.6.11",
     "squizlabs/php_codesniffer": "3.6.0",
     "php-coveralls/php-coveralls": "2.4.3",
     "vimeo/psalm": "4.10.0",