[fix] Apply class directive for <svelte:element> properly

[baseballyama]

fix: #7521

I have checked that the bug has been fixed for all of the REPLs provided by all three people through the issue.

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• Ideally, include a test that fails without this PR but passes with it.

Tests

• Run the tests with npm test and lint the project with npm run lint

[AlbertMarashi]

Any idea when this is gonna get released