Add CHANGELOG.md entry

Author: jonmmease

Diff for: CHANGELOG.md

@@ -4,6 +4,8 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 
 ## UNRELEASED
 
+### Fixed
+  - Fixed regression introduced in version 5.0.0 where pandas/numpy arrays with `dtype` of Object were being converted to `list` values when added to a Figure ([#3292](https://github.com/plotly/plotly.py/issues/3292), [#3293](https://github.com/plotly/plotly.py/pull/3293))
 
 ## [5.1.0] - 2021-06-28