Docs: Update UPGRADING.md with corrected Environment usage example

lloricode · lloricode · commit 2bac771f0d99 · 2025-08-25T18:12:55.000+08:00
diff --git a/UPGRADING.md b/UPGRADING.md
@@ -162,7 +162,7 @@ $checkout = new CheckoutDto(
 #### Environment & Config
 - **Old:**
 ```php
-Environment::SANDBOX;
+PaymayaClient::ENVIRONMENT_SANDBOX;
 ```
 - **New:**
 ```php
