Update CHANGELOG.md

Author: LiamConnors

CHANGELOG.md

@@ -2,6 +2,17 @@
 All notable changes to this project will be documented in this file.
 This project adheres to [Semantic Versioning](http://semver.org/).
 
+## Unreleased
+
+### Updated
+- Updated Plotly.js from version 2.30.0 to version 2.31.0. See the [plotly.js CHANGELOG](https://github.com/plotly/plotly.js/blob/master/CHANGELOG.md#2310----2024-04-10) for more information. These changes are reflected in the auto-generated `plotly.graph_objects` module. Notable changes include:
+  - Add `zorder` attribute to various cartesian traces for controlling stacking order of SVG traces drawn into a subplot [[#6918](https://github.com/plotly/plotly.js/pull/6918), [#6953](https://github.com/plotly/plotly.js/pull/6953)],
+    This feature was anonymously sponsored: thank you to our sponsor!
+  - Add "between" option to shape layer for placing them above grid lines and below traces [[#6927](https://github.com/plotly/plotly.js/pull/6927)],
+    with thanks to @my-tien for the contribution!
+  - Add "raw" `sizemode` to cone trace [[#6938](https://github.com/plotly/plotly.js/pull/6938)]
+  - Add `layout.hoversubplots` to enable hover effects across multiple cartesian suplots sharing one axis [[#6947](https://github.com/plotly/plotly.js/pull/6947), [#6950](https://github.com/plotly/plotly.js/pull/6950)]
+
 ## [5.20.0] - 2024-03-13
 
 ### Updated