feat: adapter-static throws buildtime error when !config.kit.prerender.default && !adapter.fallback

[elliott-with-the-longest-name-on-github]

Closes #5185.

Quite possibly the smallest git diff I've PRed recently.

There are no additional tests as I'm not sure what the best way to test this is. It'd require a new app and a test that could try to run npm run build and make sure it fails with the necessary error.

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🦋 Changeset detected

Latest commit: 019e097

The changes in this PR will be included in the next version bump.

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@sveltejs/adapter-static	Patch

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[benmccann]

should we rename the app from disabled to fallback? This test app looks a bit weird as it doesn't check any of the output or anything

[Rich-Harris]

sure, done