Update release notes

Author: itsmeichigo

RELEASE-NOTES.txt

@@ -6,6 +6,7 @@
 - [**] Order Details: Update Shipping Labels section for stores with Woo Shipping extension [https://github.com/woocommerce/woocommerce-ios/pull/15889]
 - [*] Order List: New orders made through Point of Sale are now filterable via the Order List filters menu [https://github.com/woocommerce/woocommerce-ios/pull/15910]
 - [*] Shipping Labels: Update mark order completed toggle on purchase form [https://github.com/woocommerce/woocommerce-ios/pull/15917]
+- [*] Shipping Labels: Optimize data loading on purchase form [https://github.com/woocommerce/woocommerce-ios/pull/15919]
 
 22.8
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