Update release notes

Author: itsmeichigo

RELEASE-NOTES.txt

@@ -4,6 +4,7 @@
 23.9
 -----
 - [Internal] Moved the request for push notification authorization after login [https://github.com/woocommerce/woocommerce-ios/pull/16428]
+- [Internal] Cleaned up logic for push notification token registration [https://github.com/woocommerce/woocommerce-ios/pull/16434]
 - [*] Fixed possible sync issue in POS (https://github.com/woocommerce/woocommerce-ios/pull/16423)
 
 23.8