fix: correct noindex example URL pattern typo

The previous example for matching `workers.dev`
URLs under "Prevent your workers.dev URLs showing
in search results" incorrectly used two
splats, i.e. `*`, when only one splat can be used
at maximum.

This commit updates the example to use a single
splat wildcard with a placeholder pattern that
correctly matches both `workers.dev` URLs and
Preview URLs.

Author: sibi361

src/content/partials/workers/custom_headers.mdx

@@ -117,13 +117,13 @@ This applies the `Access-Control-Allow-Origin` header to any incoming URL. To be
 
 [Google](https://developers.google.com/search/docs/advanced/robots/robots_meta_tag#directives) and other search engines often support the `X-Robots-Tag` header to instruct its crawlers how your website should be indexed.
 
-For example, to prevent your <code>{props.product === 'workers' ? '\*.workers.dev' : '\*.pages.dev'}</code> URLs from being indexed, add the following to your `_headers` file:
+For example, to prevent your <code>{props.product === 'workers' ? '\*.\*.workers.dev' : '\*.pages.dev'}</code> URLs from being indexed, add the following to your `_headers` file:
 
 <Code
 	lang="txt"
 	code={
 		props.product === "workers"
-			? `https://*.workers.dev/*\n\tX-Robots-Tag: noindex`
+			? `https://:version.:subdomain.workers.dev/*\n\tX-Robots-Tag: noindex`
 			: `https://*.pages.dev/*\n\tX-Robots-Tag: noindex`
 	}
 />