docs: update w3 slider patten link

[aquariuslt]

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This pull request:

• [ ] Fixes a bug
• [ ] Adds additional features/functionality
• [x] Updates documentation or example code
• [ ] Other

update w3.org links for slider-with-multi-thumb

preview link: https://radix-website-git-fork-aquariuslt-docs-update-w3-860835-workos.vercel.app/primitives/docs/components/slider

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Name	Status	Preview	Comments	Updated (UTC)
radix-website	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	May 19, 2024 7:10pm

[aquariuslt]

closed since https://github.com/radix-ui/website/pull/795