composer: update phpstan/phpstan-phpunit requirement

Updates the requirements on [phpstan/phpstan-phpunit](https://github.com/phpstan/phpstan-phpunit) to permit the latest version.
- [Release notes](https://github.com/phpstan/phpstan-phpunit/releases)
- [Commits](phpstan/phpstan-phpunit@2.0.12...2.0.16)

---
updated-dependencies:
- dependency-name: phpstan/phpstan-phpunit
  dependency-version: 2.0.16
  dependency-type: direct:development
...

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

Author: dependabot[bot]

composer.json

@@ -30,7 +30,7 @@
     "friendsofphp/php-cs-fixer": "^3.92",
     "ergebnis/composer-normalize": "^2.48",
     "ergebnis/php-cs-fixer-config": "^6.58",
-    "phpstan/phpstan-phpunit": "2.0.12"
+    "phpstan/phpstan-phpunit": "2.0.16"
   },
   "config": {
     "allow-plugins": {