Update dependency phpunit/phpunit to ~9.6.0

| datasource | package         | from   | to    |
| ---------- | --------------- | ------ | ----- |
| packagist  | phpunit/phpunit | 9.5.25 | 9.6.9 |


Signed-off-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

composer.json

@@ -39,7 +39,7 @@
         "laminas/laminas-coding-standard": "~2.4.0",
         "laminas/laminas-math": "~3.6.0",
         "laminas/laminas-servicemanager": "~3.19.0",
-        "phpunit/phpunit": "~9.5.25"
+        "phpunit/phpunit": "~9.6.0"
     },
     "suggest": {
         "laminas/laminas-math": "(^3.3) To support Python Pickle serialization",