Move changelog entry down to 2.x block

We need to update our PR template to suggest that people add things to
"unreleased 2.x" unless they definitely want to leave things for 3.0.

Signed-off-by: Michael Froh <froh@amazon.com>

Author: msfroh

CHANGELOG.md

@@ -98,7 +98,6 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 - [Bug] Check phase name before SearchRequestOperationsListener onPhaseStart ([#12035](https://github.com/opensearch-project/OpenSearch/pull/12035))
 - Fix Span operation names generated from RestActions ([#12005](https://github.com/opensearch-project/OpenSearch/pull/12005))
 - Fix error in RemoteSegmentStoreDirectory when debug logging is enabled ([#12328](https://github.com/opensearch-project/OpenSearch/pull/12328))
-- Fix UOE While building Exists query for nested search_as_you_type field ([#12048](https://github.com/opensearch-project/OpenSearch/pull/12048))
 
 ### Security
 
@@ -128,6 +127,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 
 ### Fixed
 - Fix issue with feature flags where default value may not be honored ([#12849](https://github.com/opensearch-project/OpenSearch/pull/12849))
+- Fix UOE While building Exists query for nested search_as_you_type field ([#12048](https://github.com/opensearch-project/OpenSearch/pull/12048))
 
 ### Security