composer(deps-dev): update phpunit/phpunit requirement

Updates the requirements on [phpunit/phpunit](https://github.com/sebastianbergmann/phpunit) to permit the latest version.
- [Changelog](https://github.com/sebastianbergmann/phpunit/blob/10.2.6/ChangeLog-10.2.md)
- [Commits](sebastianbergmann/phpunit@10.2.3...10.2.6)

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

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

composer.json

@@ -44,7 +44,7 @@
     "phpstan/phpstan": "^1.10.23",
     "phpstan/phpstan-deprecation-rules": "^1.1.3",
     "phpstan/phpstan-phpunit": "^1.3.13",
-    "phpunit/phpunit": "^10.2.3",
+    "phpunit/phpunit": "^10.2.6",
     "rector/rector": "^0.17.2",
     "vimeo/psalm": "^5.13.1"
   },