Update CHANGELOG.md (#42076)

Author: lzchen

sdk/monitor/azure-monitor-opentelemetry-exporter/CHANGELOG.md

@@ -1,6 +1,6 @@
 # Release History
 
-## 1.0.0b40 (Unreleased)
+## 1.0.0b40 (2025-07-17)
 
 ### Features Added
 
@@ -14,12 +14,6 @@
   ([#41971](https://github.com/Azure/azure-sdk-for-python/pull/41971))
 
 
-### Breaking Changes
-
-### Bugs Fixed
-
-### Other Changes
-
 ## 1.0.0b39 (2025-06-25)
 
 ### Bugs Fixed