composer: update phpstan/phpstan-phpunit requirement from 2.0.7 to 2.0.8 (#17)

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@2.0.7...2.0.8)

---
updated-dependencies:
- dependency-name: phpstan/phpstan-phpunit
  dependency-version: 2.0.8
  dependency-type: direct:development
...

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

Author: dependabot[bot]

composer.json

@@ -20,7 +20,7 @@
         "friendsofphp/php-cs-fixer": "^3.89",
         "ergebnis/composer-normalize": "^2.48",
         "ergebnis/php-cs-fixer-config": "^6.56",
-        "phpstan/phpstan-phpunit": "2.0.7"
+        "phpstan/phpstan-phpunit": "2.0.8"
     },
     "autoload": {
         "psr-4": {