fix: add pending snippet to <svelte:boundary> types (#16379)

* add pending snippet to  <svelte:boundary> types

* Update .changeset/many-bats-juggle.md

---------

Co-authored-by: jayce jones <jayce.jones@trinityonline.com>
Co-authored-by: Rich Harris <hello@rich-harris.dev>

.changeset/many-bats-juggle.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: add `pending` snippet to `<svelte:boundary>` types

packages/svelte/elements.d.ts

@@ -2080,6 +2080,7 @@ export interface SvelteHTMLElements {
 	'svelte:boundary': {
 		onerror?: (error: unknown, reset: () => void) => void;
 		failed?: import('svelte').Snippet<[error: unknown, reset: () => void]>;
+		pending?: import('svelte').Snippet;
 	};
 
 	[name: string]: { [name: string]: any };