Fix vite HMR port using nginx without router

What does this merge request do and why?

This fixes that the vite HMR doesn’t work when using nginx without the router.

This is a regression from !4262 (merged).

How to set up and validate locally

1. Enable vite: gdk config set vite.enabled
2. Disable webpack: gdk config set webpack.enabled false
3. Enable nginx: gdk config set nginx.enabled true
4. Disable the router: gdk config set gitlab_http_router.enabled false
5. gdk reconfigure
6. gdk start
7. gdk open
8. Open the DevTools
9. See that the websocket request to /vite-dev/ succeeds

Impacted categories

The following categories relate to this merge request:

• gdk-reliability - e.g. When a GDK action fails to complete.
• gdk-usability - e.g. Improvements or suggestions around how the GDK functions.
• gdk-performance - e.g. When a GDK action is slow or times out.

Merge request checklist

• This change is backward compatible. If not, please include steps to communicate to our users.
• Tests added for new functionality. If not, please raise an issue to follow-up.
• Documentation added/updated, if needed.
• Announcement added, if change is notable.
• gdk doctor test added, if needed.