docs(x/authz): update changelog to include API breaking events change…

… (backport #21522) (#21538)

Co-authored-by: Matt Kocubinski <mkocubinski@gmail.com>

x/authz/CHANGELOG.md

@@ -44,6 +44,7 @@ Ref: https://keepachangelog.com/en/1.0.0/
     * `ExportGenesis` also returns an error.
     * `IterateGrants` returns an error, its handler function also returns an error.
 * [#19637](https://github.com/cosmos/cosmos-sdk/pull/19637) `NewKeeper` doesn't take a message router anymore. Set the message router in the `appmodule.Environment` instead.
+    * `Exec` no longer emits duplicate events containing a "authz_msg_index" attribute.
 * [#19490](https://github.com/cosmos/cosmos-sdk/pull/19490) `appmodule.Environment` is received on the Keeper to get access to different application services.
 * [#18737](https://github.com/cosmos/cosmos-sdk/pull/18737) Update the keeper method `DequeueAndDeleteExpiredGrants` to take a limit argument for the number of grants to prune.
 * [#16509](https://github.com/cosmos/cosmos-sdk/pull/16509) `AcceptResponse` has been moved to sdk/types/authz and the `Updated` field is now of the type `sdk.Msg` instead of `authz.Authorization`.