Updates: (deps): 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@1.3.15...1.3.16)

---
updated-dependencies:
- dependency-name: phpstan/phpstan-phpunit
  dependency-type: direct:production
...

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

composer.json

@@ -17,7 +17,7 @@
     "phpstan/extension-installer": "1.3.1",
     "phpstan/phpstan": "~1.10.35",
     "phpstan/phpstan-deprecation-rules": "^1.0",
-    "phpstan/phpstan-phpunit": "1.3.15",
+    "phpstan/phpstan-phpunit": "1.3.16",
     "phpspec/prophecy-phpunit": "v2.0.2",
     "goalgorilla/open_social_scripts": "~4.0.0",
     "symfony/phpunit-bridge": "^4.4 || ^5.4 || ^6.2"