Update dependency phpunit/phpunit to v12

Author: renovate[bot]

composer.json

@@ -8,7 +8,7 @@
         "composer/installers": "^1.0"
     },
     "require-dev": {
-        "phpunit/phpunit": "^9.6",
+        "phpunit/phpunit": "^12.0",
         "mockery/mockery": "^1.5",
         "wp-phpunit/wp-phpunit": "^6.1",
         "yoast/phpunit-polyfills": "^1.0",