Add changelog entry

Author: jsnajdr

packages/components/CHANGELOG.md

@@ -28,6 +28,7 @@
 
 -   `SlotFill`: rewrite the non-portal version to use `observableMap` ([#67400](https://github.com/WordPress/gutenberg/pull/67400)).
 -   `DatePicker`: Prepare day buttons for 40px default size ([#68156](https://github.com/WordPress/gutenberg/pull/68156)).
+-   `SlotFill`: register slots in a layout effect ([#68176](https://github.com/WordPress/gutenberg/pull/68176)).
 
 ## 29.0.0 (2024-12-11)