Move changelog entry down to 2.x block (opensearch-project#13004)

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>
Signed-off-by: Shivansh Arora <hishiv@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