[docs] clear timeout on destroy

backported from https://github.com/sveltejs/learn.svelte.dev/pull/166

site/content/tutorial/12-actions/02-adding-parameters-to-actions/app-a/longpress.js

@@ -18,6 +18,7 @@ export function longpress(node, duration) {
 
 	return {
 		destroy() {
+			clearTimeout(timer);
 			node.removeEventListener('mousedown', handleMousedown);
 			node.removeEventListener('mouseup', handleMouseup);
 		}

site/content/tutorial/12-actions/02-adding-parameters-to-actions/app-b/longpress.js

@@ -21,6 +21,7 @@ export function longpress(node, duration) {
 			duration = newDuration;
 		},
 		destroy() {
+			clearTimeout(timer);
 			node.removeEventListener('mousedown', handleMousedown);
 			node.removeEventListener('mouseup', handleMouseup);
 		}