[DOCS] fix link in contributing.md

[gap-editor]

PR-Codex overview

This PR updates the link in the .github/contributing.md file to correctly point to the consolidated SDK project directory.

Detailed summary

• Updated the link to the consolidated SDK project from [/packages/thirdweb](./packages/thirdweb) to [/packages/thirdweb](../packages/thirdweb) for accuracy.

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[changeset-bot]

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Latest commit: 2b157ba

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[vercel]

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[joaquim-verges]

thank you @gap-editor !