Update phpstan/phpstan requirement from 2.0.2 to 2.0.3 (#151)

Author: dependabot[bot]

composer.json

@@ -11,7 +11,7 @@
         "nethergamesmc/quiche": "dev-master"
     },
     "require-dev": {
-        "phpstan/phpstan": "2.0.2",
+        "phpstan/phpstan": "2.0.3",
         "nethergamesmc/pocketmine-mp": "dev-stable"
     },
     "repositories": [