fix: avoid copying unused SSR stylesheets to client assets

[eltigerchino]

fixes #9161

This PR avoids copying the unused SSR stylesheets that are generated from Vite's build.ssrEmitAssets option to the client assets folder. Since SvelteKit only links to the client stylesheets in each page, these SSR stylesheets shouldn't be copied over.

related #10686

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Latest commit: 8b24a70

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