adapter-static (SPA mode): index.html not generated when prerender.enabled = false

[UltraCakeBakery]

Describe the bug
The following config causes adapter-static -> npm run build to not include the root index.html file - the one that you always send to the client - as specified in the adapter settings object, which is required to actually load the SPA.

import adapter from '@sveltejs/adapter-static';

/** @type {import('@sveltejs/kit').Config} */
const config = {
	kit: {
		adapter: adapter({
			fallback: 'index.html'
		}),
		ssr: false,
		prerender: {
			enabled: false
		}
	}
};

export default config;

Logs
N/A

To Reproduce

1. npm init svelte@next
2. select the skeleton project, say no to everything typescript etc.
3. copy paste my config and install the static adapter

Expected behavior
I don't the file to not be included when disabling prerendering. It would make even more sense for it to be required to be set to false for the files to be generated.

Stacktraces
N\A

Severity
On a scale from 1 to 10, maybe a 3.3? I have no idea as this might be intended behavior that I am not aware off.

[UltraCakeBakery]

Another way to describe this issue:

The fallback option file is not generated when prerender.enabled is false

[Conduitry]

Sounds like a duplicate of #1588.