[12.x] use type declaration on property (#53970)

* use type declaration on property

also use promoted property

* restore comment

src/Illuminate/Bus/Events/BatchDispatched.php

@@ -6,21 +6,14 @@
 
 class BatchDispatched
 {
-    /**
-     * The batch instance.
-     *
-     * @var \Illuminate\Bus\Batch
-     */
-    public $batch;
-
     /**
      * Create a new event instance.
      *
-     * @param  \Illuminate\Bus\Batch  $batch
+     * @param  \Illuminate\Bus\Batch  $batch  The batch instance.
      * @return void
      */
-    public function __construct(Batch $batch)
-    {
-        $this->batch = $batch;
+    public function __construct(
+        public Batch $batch,
+    ) {
     }
 }