changelog: add entry back (#5738)

## Description

add back removed changelog entry

Closes: #XXX

CHANGELOG_PENDING.md

@@ -13,6 +13,8 @@ Friendly reminder, we have a [bug bounty program](https://hackerone.com/tendermi
   - [config] \#5728 `fast_sync = "v1"` is no longer supported (@melekes)
 
 - Apps
+  - [ABCI] \#5447 Remove `SetOption` method from `ABCI.Client` interface
+  - [ABCI] \#5447 Reset `Oneof` indexes for  `Request` and `Response`.
 
 - P2P Protocol
 

UPGRADING.md

@@ -8,6 +8,8 @@ This guide provides instructions for upgrading to specific versions of Tendermin
 
 * Added `AbciVersion` to `RequestInfo`. Applications should check that the ABCI version they expect is being used in order to avoid unimplemented changes errors.
 
+* The method `SetOption` has been removed from the ABCI.Client interface. This feature was used in the early ABCI implementation's. 
+
 ### Config Changes
 
 * `fast_sync = "v1"` is no longer supported. Please use `v2` instead.