chore: improved storybook prefetching

[manuel3108]

Relates #622
Relates sveltejs/svelte-ecosystem-ci#32

In direct comparison to #622 this has the disadvantage, that this also run's locally. We could check via the CI env variable, but I don't think that would help to reproduce pipeline failures locally. On the other hand, this is an improvement in comparison to #622 because it allows our tests to be run everywhere, without requiring explicit setup. This is in example the case in svelte-ecosystem-ci (sveltejs/svelte-ecosystem-ci#32)

If this works the way I think it should (I will check in the pipeline), I would personally consider this as a slight improvement.

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