add changelog

Author: thomas-nguy

CHANGELOG.md

@@ -36,6 +36,13 @@ Ref: https://keepachangelog.com/en/1.0.0/
 
 # Changelog
 
+## UNRELEASED
+
+### Bug Fixes
+* (mempool) [#25563](https://github.com/cosmos/cosmos-sdk/pull/25563) Cleanup sender indices in case of tx replacement.
+
+
+
 ## [v0.53.4](https://github.com/cosmos/cosmos-sdk/releases/tag/v0.53.3) - 2025-07-25
 
 This patch update also includes minor dependency bumps.