chore: Prepare changelog for 1.6.0 release (#40863)

Author: kdestin

sdk/evaluation/azure-ai-evaluation/CHANGELOG.md

@@ -1,6 +1,6 @@
 # Release History
 
-## 1.6.0 (Unreleased)
+## 1.6.0 (2025-05-07)
 
 ### Features Added
 - New `<evaluator>.binary_aggregate` field added to evaluation result metrics. This field contains the aggregated binary evaluation results for each evaluator, providing a summary of the evaluation outcomes.
@@ -22,8 +22,6 @@
     Now, users may import data containing fields with numeric characters. 
 
 
-### Other Changes
-
 ## 1.5.0 (2025-04-04)
 
 ### Features Added