[HUDI-1992] Release the new records map for merge handle #close (#3056)

hudi-client/hudi-client-common/src/main/java/org/apache/hudi/io/HoodieMergeHandle.java

@@ -344,6 +344,7 @@ public class HoodieMergeHandle<T extends HoodieRecordPayload, I, K, O> extends H
         }
       }
 
+      keyToNewRecords.clear();
       ((ExternalSpillableMap) keyToNewRecords).close();
       writtenRecordKeys.clear();