Update dependency phpstan/phpstan to ^2.1.6

| datasource | package         | from  | to    |
| ---------- | --------------- | ----- | ----- |
| packagist  | phpstan/phpstan | 2.1.5 | 2.1.6 |

Author: renovate[bot]

composer.json

@@ -19,7 +19,7 @@
     ],
     "require": {
         "php": "~8.3.0 || ~8.4.0",
-        "phpstan/phpstan": "^2.1.5"
+        "phpstan/phpstan": "^2.1.6"
     },
     "require-dev": {
         "laminas/laminas-filter": "^2.40.0",