Update changelog

CHANGELOG.md

@@ -16,6 +16,7 @@
 - The `invalid` prop now reflects the control's validity as determined by the browser's constraint validation API
 - Added `required` to `sl-checkbox`, `sl-select`, and `sl-switch`
 - Added `reportValidity()` and `setCustomValidity()` methods to all form controls
+- Added validation checking for custom and native form controls to `sl-form`
 - Removed the `valid` prop from all form controls
 - Removed valid and invalid design tokens and related styles (you can use your own custom styles to achieve this)