Group unreleased changelog items more appropriately

The items were all listed under the "Added" heading, but I'm pretty
confident #976 & #991 were effectively internal fixes that had no impact
on clients of the web component, and it feels like it's worth
highlighting #1003 as a *change* to the existing behaviour rather than
the addition of a new feature.

Author: floehopper

CHANGELOG.md

@@ -9,12 +9,18 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 ### Added
 
 - Support to enable embedding iframes in HTML projects from in-house domains (#985)
-- Unit tests for `pyodide` runner (#976)
 - Dispatch event when project identifier changes, e.g. after project is remixed (#2830)
-- Remove broken `format` script (#991)
-- Invalidate cached project when project is remixed (#1003)
 - Add `load_remix_disabled` attribute to web component (#992)
 
+### Changed
+
+- Invalidate cached project when project is remixed (#1003)
+
+### Fixed
+
+- Unit tests for `pyodide` runner (#976)
+- Remove broken `format` script (#991)
+
 ## [0.22.2] - 2024-03-18
 
 ### Added