Modify changelog file.

CHANGELOG.md

@@ -153,6 +153,7 @@ Ref: https://keepachangelog.com/en/1.0.0/
 
 ### Client Breaking Changes
 
+* (x/staking) [#15701](https://github.com/cosmos/cosmos-sdk/pull/15701) `HistoricalInfoKey` now has a binary format.
 * (grpc-web) [#14652](https://github.com/cosmos/cosmos-sdk/pull/14652) Use same port for gRPC-Web and the API server.
 
 ### CLI Breaking Changes
@@ -308,6 +309,7 @@ Ref: https://keepachangelog.com/en/1.0.0/
 
 ### State Machine Breaking
 
+* (x/staking) [#15701](https://github.com/cosmos/cosmos-sdk/pull/15701) The `HistoricalInfoKey` has been updated to use a binary format.
 * (baseapp, x/auth/posthandler) [#13940](https://github.com/cosmos/cosmos-sdk/pull/13940) Update `PostHandler` to receive the `runTx` success boolean.
 * (store) [#14378](https://github.com/cosmos/cosmos-sdk/pull/14378) The `CacheKV` store is thread-safe again, which includes improved iteration and deletion logic. Iteration is on a strictly isolated view now, which is breaking from previous behavior.
 * (x/bank) [#14538](https://github.com/cosmos/cosmos-sdk/pull/14538) Validate denom in bank balances GRPC queries.