fix: add pending snippet to <svelte:boundary> types

packages/svelte/svelte-html.d.ts

@@ -247,6 +247,7 @@ declare global {
 			'svelte:boundary': {
 				onerror?: (error: unknown, reset: () => void) => void;
 				failed?: import('svelte').Snippet<[error: unknown, reset: () => void]>;
+				pending?: import('svelte').Snippet;
 			};
 			// don't type svelte:options, it would override the types in svelte/elements and it isn't extendable anyway