docs: add PR link to changelog entry for Mantle gas fee flow

Author: jeremy-consensys

packages/transaction-controller/CHANGELOG.md

@@ -9,7 +9,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Added
 
-- Add Mantle layer 1 gas fee flow with tokenRatio conversion for accurate MNT-denominated gas estimates
+- Add Mantle layer 1 gas fee flow with tokenRatio conversion for accurate MNT-denominated gas estimates ([#8376](https://github.com/MetaMask/core/pull/8376))
 
 ### Changed