chore: update changelog

Author: gadomski

CHANGES.md

@@ -26,6 +26,7 @@
 * Manually exclude non-truthy optional values from sqlalchemy serialization of Collections ([#508](https://github.com/stac-utils/stac-fastapi/pull/508))
 * Support `intersects` in GET requests ([#521](https://github.com/stac-utils/stac-fastapi/pull/521))
 * Deleting items that had repeated ids in other collections ([#520](https://github.com/stac-utils/stac-fastapi/pull/520))
+* 404 for missing collection on /items for sqlalchemy ([#528](https://github.com/stac-utils/stac-fastapi/pull/528))
 
 ### Deprecated