fix: sitemap_index.xml collides with server/routes/s/** server route

[gavin667]

🐛 The bug

We have a catch all "shortlink" URL that lives under domain-here.com/s/any-path-or-folder-can-go-here.

When we have multi sitemaps we get the sitemap_index.xml file which is accessible locally under domain-here.com/sitemap_index.xml but when building for production it returns the response from server/routes/s/[...].get.js.

This can be seen here - https://nuxt-3-colliding-server-route.vercel.app/sitemap_index.xml (using the reproduction repo linked below)

🛠️ To reproduce

You can clone https://github.com/gavin667/nuxt-3-colliding-server-route, run npm run build, PORT=3001 node .output/server/index.mjs then access at http://localhost:3001/sitemap_index.xml

🌈 Expected behavior

I would expect to be able to access sitemap_index.xml in both local and production builds.

ℹ️ Additional context

No response