feat: Update package.json to 2.2.4

src/UniTask/Assets/Plugins/UniTask/package.json

 {
     "name": "com.cysharp.unitask",
     "displayName": "UniTask",
-    "version": "2.2.3",
+    "version": "2.2.4",
     "unity": "2018.4",
     "description": "Provides an efficient async/await integration to Unity.",
     "keywords": [ "async/await", "async", "Task", "UniTask" ],