Update phpunit/phpunit requirement from ^9.5 to ^11.4

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/11.4.0/ChangeLog-11.4.md)
- [Commits](sebastianbergmann/phpunit@9.5.0...11.4.0)

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

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

composer.json

@@ -27,7 +27,7 @@
         "oxid-esales/oxideshop-ce": "<7.0.0-rc.2"
     },
     "require-dev": {
-        "phpunit/phpunit": "^9.5",
+        "phpunit/phpunit": "^11.4",
         "phpstan/phpstan": "^1.8.10",
         "squizlabs/php_codesniffer": "3.*",
         "phpmd/phpmd": "^2.11"