fix: Address bugs in SvelteKit “Preloading” tutorial example (#1334)

Fix the tutorial code: kit/preload

Correctly capture the previous navigation state.

Co-authored-by: Tee Ming <[email protected]>

Author: BioniCosmos

apps/svelte.dev/content/tutorial/04-advanced-sveltekit/03-link-options/01-preload/+assets/app-a/src/routes/+layout.svelte

@@ -11,7 +11,7 @@
 		if (navigating.to) {
 			start = Date.now();
 			end = null;
-			previous = navigating;
+			previous = { ...navigating };
 		} else {
 			end = Date.now();
 		}

apps/svelte.dev/content/tutorial/04-advanced-sveltekit/03-link-options/01-preload/+assets/app-b/src/routes/+layout.svelte

@@ -11,7 +11,7 @@
 		if (navigating.to) {
 			start = Date.now();
 			end = null;
-			previous = navigating;
+			previous = { ...navigating };
 		} else {
 			end = Date.now();
 		}