Chore(deps-dev): Update phpunit/phpunit requirement

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/12.3.0/ChangeLog-12.3.md)
- [Commits](https://github.com/sebastianbergmann/phpunit/compare/9.0.0...12.3.0)

---
updated-dependencies:
- dependency-name: phpunit/phpunit
  dependency-version: 12.3.0
  dependency-type: direct:development
...

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

tests/integration/composer.json

@@ -1,6 +1,6 @@
 {
     "require-dev": {
-        "phpunit/phpunit": "~9",
+        "phpunit/phpunit": "~12",
         "behat/behat": "~3.23.0",
         "guzzlehttp/guzzle": "7.9.2",
         "jarnaiz/behat-junit-formatter": "^1.3",