Update to PHPStan 2.

Author: Crell

composer.json

@@ -32,7 +32,7 @@
         "phpunit/phpunit": "^7.0 || ^8.0 || ^9.0",
         "psr/http-factory": "^1.0",
         "psr/http-message": "1.*",
-        "phpstan/phpstan": "^1.3"
+        "phpstan/phpstan": "^2.1"
     },
     "extra": {
         "branch-alias": {