[fix] no root node for detached dom node

[tanhauhau]

Fixes #6567

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Tests

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

[baseballyama]

@tanhauhau

hi. This is just a curious question.
I'm happy if you answer my question🙏

I also tried to fix this issue but I couldn't reproduce the issue in my local environment.
So how did you reproduce it in your local environment?

(And also I could reproduce it on Codepen and Svelte REPL but in this case, I couldn't check behavior after fixing code by my knowledge...)

[jacwright]

This breaks transitions/animations in iframes (see #3625). Please return ownerDocument, not document.

return node.ownerDocument;

Once fixed, you can close #6637 😄