Update CHANGELOG.md (#749)

Author: lovelydinosaur

CHANGELOG.md

@@ -4,6 +4,10 @@ All notable changes to this project will be documented in this file.
 
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 
+## Unreleased
+
+- Handle HTTP/1.1 half-closed connections gracefully. (#641)
+
 ## 0.17.3 (5th July 2023)
 
 - Support async cancellations, ensuring that the connection pool is left in a clean state when cancellations occur. (#726)