add fix to changelog

Author: edgarriba

CHANGELOG.md

@@ -257,6 +257,9 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 - Fixed `BaseFinetuning` callback to properly handle parent modules w/ parameters ([#7931](https://github.com/PyTorchLightning/pytorch-lightning/pull/7931))
 
 
+- Fixes access to callback_metrics in ddp_spawn ([#7916](https://github.com/PyTorchLightning/pytorch-lightning/pull/7916)) 
+
+
 ## [1.3.5] - 2021-06-08
 
 ### Added