Update phpstan

Author: nikic

composer.json

@@ -9,7 +9,7 @@
   },
   "require-dev": {
     "phpunit/phpunit": "^9",
-    "phpstan/phpstan": "^1.10"
+    "phpstan/phpstan": "^2.1"
   },
   "suggest": {
     "ext-pcntl": "Needed for timeout support"