update changelog

Author: Conduitry

CHANGELOG.md

@@ -9,6 +9,7 @@
 * Add missing function overload for `derived` to allow explicitly setting an initial value for non-async derived stores ([#6172](https://github.com/sveltejs/svelte/pull/6172))
 * Fix scope leak when updating an `{#await}` block ([#6173](https://github.com/sveltejs/svelte/issues/6173))
 * Pass full markup source to `script`/`style` preprocessors ([#6169](https://github.com/sveltejs/svelte/pull/6169))
+* Fix `crossfade` types to mark `fallback` as optional ([#6201](https://github.com/sveltejs/svelte/pull/6201))
 * Add missing "context" typing to `SvelteComponent` constructor options ([#6236](https://github.com/sveltejs/svelte/pull/6236))
 * Don't automatically switch to `svg` namespace when in `foreign` namespace ([#6257](https://github.com/sveltejs/svelte/issues/6257))