Add changelog

Author: aaronrobertshaw

packages/components/CHANGELOG.md

@@ -7,6 +7,8 @@
 -   `BorderControl`: Improve labelling, tooltips and DOM structure ([#42348](https://github.com/WordPress/gutenberg/pull/42348/)).
 -   `BaseControl`: Set zero padding on `StyledLabel` to ensure cross-browser styling ([#42348](https://github.com/WordPress/gutenberg/pull/42348/)).
 -   `UnitControl`: Update unit select's focus styles to match input's ([#42383](https://github.com/WordPress/gutenberg/pull/42383)).
+-   `BorderControl`: Render dropdown as prefix within its `UnitControl` ([#42212](https://github.com/WordPress/gutenberg/pull/42212/))
+-   `UnitControl`: Update prop types to allow ReactNode as prefix ([#42212](https://github.com/WordPress/gutenberg/pull/42212/))
 
 ### Internal