Update dependency phpunit/phpunit to ^12.5.6

| datasource | package         | from   | to     |
| ---------- | --------------- | ------ | ------ |
| packagist  | phpunit/phpunit | 12.5.5 | 12.5.6 |

Author: renovate[bot]

composer.json

@@ -30,7 +30,7 @@
         "doctrine/coding-standard": "^14.0.0",
         "justinrainbow/json-schema": "^6.6.4",
         "php-standard-library/psalm-plugin": "^2.3.0",
-        "phpunit/phpunit": "^12.5.5",
+        "phpunit/phpunit": "^12.5.6",
         "psalm/plugin-phpunit": "^0.19.5",
         "roave/infection-static-analysis-plugin": "^1.43.0",
         "roave/security-advisories": "dev-master",