Add to CHANGELOG

Signed-off-by: Craig Perkins <[email protected]>

Author: cwperks

CHANGELOG.md

@@ -10,6 +10,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 - Bump `org.apache.commons:commons-lang3` from 3.14.0 to 3.15.0 ([#14861](https://github.com/opensearch-project/OpenSearch/pull/14861))
 
 ### Changed
+- Make ThreadContext.markAsSystemContext package-private ([#14988](https://github.com/opensearch-project/OpenSearch/pull/14988))
 
 ### Deprecated