require more recent phpstan

phpstsan <2.1.11 and >=2.1.11 give different results; if we're testing for specific results, we need to pick one

Author: shish

composer.json

@@ -11,7 +11,7 @@
     ],
     "require": {
         "php": "^8.1",
-        "phpstan/phpstan": "^2.0",
+        "phpstan/phpstan": "^2.1.11",
         "thecodingmachine/safe": "^1.2 || ^2.0 || ^3.0",
         "nikic/php-parser": "^5"
     },