Update phpstan-8.yaml

Author: gplanchat

.github/workflows/phpstan-8.yaml

@@ -14,7 +14,7 @@ jobs:
       - uses: php-actions/composer@v5
         with:
           args: --prefer-dist
-          php_version: 8.0
+          php_version: 8.1
 
       - name: PHPStan
         uses: php-actions/phpstan@v2