Add Breaking Changes in history.md

Author: iwanttobepowerful

site/_docs/history.md

@@ -49,6 +49,11 @@ other software versions as specified in gradle.properties.
 #### Breaking Changes
 {: #breaking-1-42-0}
 
+* [<a href="https://issues.apache.org/jira/browse/CALCITE-6942">CALCITE-6942</a>]
+Modify the access level of the method `decorrelateSortAsAggregate` from `protected` to `private`.
+Rename the method `decorrelateFetchOneSort` to `decorrelateSortWithRowNumber`,
+and adjust its access modifier from `protected` to `private` accordingly.
+
 #### New features
 {: #new-features-1-42-0}