Update phpunit/phpunit requirement from ^9.6 to ^11.3

Updates the requirements on [phpunit/phpunit](https://github.com/sebastianbergmann/phpunit) to permit the latest version.
- [Release notes](https://github.com/sebastianbergmann/phpunit/releases)
- [Changelog](https://github.com/sebastianbergmann/phpunit/blob/11.3.1/ChangeLog-11.3.md)
- [Commits](sebastianbergmann/phpunit@9.6.0...11.3.1)

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

Signed-off-by: dependabot[bot] <[email protected]>

composer.json

@@ -42,7 +42,7 @@
  "phpstan/phpstan-phpunit": "^1.4",
  "phpstan/phpstan-strict-rules": "^1.6",
  "phpstan/extension-installer": "^1.3",
- "phpunit/phpunit" : "^9.6"
+ "phpunit/phpunit" : "^11.3"
  },
  "scripts": {
  "phpstan": [