Fix: [slug].tsx in wordpress example (#41074)

Fixing the image URL in the meta property og:image

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## Documentation / Examples

- [x] Make sure the linting passes by running `pnpm lint`
- [x] The "examples guidelines" are followed from [our contributing
doc](https://github.com/vercel/next.js/blob/canary/contributing/examples/adding-examples.md)

examples/cms-wordpress/pages/posts/[slug].tsx

@@ -37,7 +37,7 @@ export default function Post({ post, posts, preview }) {
                 </title>
                 <meta
                   property="og:image"
-                  content={post.featuredImage?.sourceUrl}
+                  content={post.featuredImage?.node.sourceUrl}
                 />
               </Head>
               <PostHeader