Update phpunit/phpunit requirement

---
updated-dependencies:
- dependency-name: phpunit/phpunit
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <support@github.com>

composer.json

@@ -28,7 +28,7 @@
     },
     "require-dev": {
         "laravel/slack-notification-channel": "^1.0|^2.0|^3.2",
-        "phpunit/phpunit": "^6.0|^7.0|^8.0|^9.0|^10.5",
+        "phpunit/phpunit": "^11.2.9",
         "squizlabs/php_codesniffer": "~2.3|^3.6",
         "orchestra/testbench": "^4.0|^5.0|^6.0|^7.0|^8.0|^9.0",
         "mockery/mockery": "^1.2"