Update phpstan/phpstan-phpunit requirement from 0.12.17 to 0.12.18 (#10)

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@0.12.17...0.12.18)

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

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

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

composer.json

@@ -24,7 +24,7 @@
         "kwn/php-rdkafka-stubs": "^2.0",
         "phpstan/extension-installer": "^1.1",
         "phpstan/phpstan": "0.12.68",
-        "phpstan/phpstan-phpunit": "0.12.17",
+        "phpstan/phpstan-phpunit": "0.12.18",
         "phpstan/phpstan-strict-rules": "0.12.9",
         "phpunit/phpunit": "^9.2",
         "psalm/plugin-phpunit": "^0.16.1",