docs: clarify transaction recipe order ID handling

Signed-off-by: memleakd <121398829+memleakd@users.noreply.github.com>

Author: memleakd

user_guide_src/source/database/transactions/013.php

@@ -4,15 +4,19 @@
 
 $orderId = $this->db->transaction(static function ($db) use ($order): int {
     $db->table('orders')->insert($order);
-    $orderId = $db->insertID();
+    $insertedOrderId = $db->insertID();
 
-    $db->afterCommit(static function () use ($orderId): void {
+    $db->afterCommit(static function () use ($insertedOrderId): void {
         service('cache')->delete('orders_list');
-        Events::trigger('order_created', $orderId);
+        Events::trigger('order_created', $insertedOrderId);
 
         // Dispatch a queued job or send a notification here.
         // The new order is committed and visible to other database connections.
     });
 
-    return $orderId;
+    return $insertedOrderId;
 });
+
+if ($orderId === false) {
+    // Handle the transaction failure.
+}