hardcode lastUpdated

Author: KianNH

src/content/docs/style-guide/fixtures/markdown.mdx

@@ -1,6 +1,7 @@
 ---
 title: Markdown
 noindex: true
+lastUpdated: 2025-01-01T00:00:00Z
 sidebar:
   hidden: true
 ---

worker/index.worker.test.ts

@@ -270,6 +270,7 @@ describe("Cloudflare Docs", () => {
 				"---
 				title: Markdown · Cloudflare Style Guide
 				description: The HTML generated by this file is used as a test fixture for our Markdown generation.
+				lastUpdated: 2025-01-01T00:00:00.000Z
 				source_url:
 				  html: http://fakehost/style-guide/fixtures/markdown/index.md
 				  md: http://fakehost/style-guide/fixtures/markdown/