[PHP]: Update phpunit/phpunit requirement in /vendor-bin/phpunit

Updates the requirements on [phpunit/phpunit](https://github.com/sebastianbergmann/phpunit) to permit the latest version.
- [Changelog](https://github.com/sebastianbergmann/phpunit/blob/9.6.16/ChangeLog-9.6.md)
- [Commits](sebastianbergmann/phpunit@9.6.15...9.6.16)

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

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

vendor-bin/phpunit/composer.json

@@ -4,7 +4,7 @@
         "vimeo/psalm": "5.20.0",
         "psalm/plugin-phpunit": "0.18.4",
         "weirdan/doctrine-psalm-plugin": "2.9.0",
-        "phpunit/phpunit": "9.6.15"
+        "phpunit/phpunit": "9.6.16"
     },
     "config": {
         "allow-plugins": {