doc: fix example of parsing request.url

PR-URL: #31302
Fixes: #31301
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Tiancheng "Timothy" Gu <timothygu99@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>

doc/api/http.md

@@ -1990,7 +1990,7 @@ When `request.url` is `'/status?name=ryan'` and
 
 ```console
 $ node
-> new URL(request.url, request.headers.host)
+> new URL(request.url, `http://${request.headers.host}`)
 URL {
   href: 'http://localhost:3000/status?name=ryan',
   origin: 'http://localhost:3000',