fix: allow self-closing tags within math namespace

[dummdidumm]

fixes #15757

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[changeset-bot]

🦋 Changeset detected

Latest commit: 2d9b1c8

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

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[svelte-docs-bot]

Preview: https://svelte-dev-git-preview-svelte-15761-svelte.vercel.app/

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Playground

pnpm add https://pkg.pr.new/svelte@15761