move changelog to API-breaking section

CHANGELOG.md

@@ -44,6 +44,7 @@ Ref: https://keepachangelog.com/en/1.0.0/
 
 ### API Breaking Changes
 
+* [\#9628](https://github.com/cosmos/cosmos-sdk/pull/9628) Rename `x/{mod}/legacy` to `x/{mod}/migrations`.
 * [\#9571](https://github.com/cosmos/cosmos-sdk/pull/9571) Implemented error handling for staking hooks, which now return an error on failure.
 * [\#9427](https://github.com/cosmos/cosmos-sdk/pull/9427) Move simapp `FundAccount` and `FundModuleAccount` to `x/bank/testutil`
 * (client/tx) [\#9421](https://github.com/cosmos/cosmos-sdk/pull/9421/) `BuildUnsignedTx`, `BuildSimTx`, `PrintUnsignedStdTx` functions are moved to
@@ -59,7 +60,6 @@ Ref: https://keepachangelog.com/en/1.0.0/
 
 ### Improvements
 
-* [\#9628](https://github.com/cosmos/cosmos-sdk/pull/9628) Rename `x/{mod}/legacy` to `x/{mod}/migrations`.
 * (cli) [\#9593](https://github.com/cosmos/cosmos-sdk/pull/9593) Check if chain-id is blank before verifying signatures in multisign and error.
 
 ### Bug Fixes