chore(deps): update dependency phpunit/phpunit to v12

Author: renovate[bot]

providers/GoFeatureFlag/composer.json

@@ -23,7 +23,7 @@
     "psr/http-message": "^2.0"
   },
   "require-dev": {
-    "phpunit/phpunit": "^9",
+    "phpunit/phpunit": "^12",
     "mockery/mockery": "^1.6",
     "spatie/phpunit-snapshot-assertions": "^4.2",
     "phan/phan": "^5.4",