React: Update vitest imports

[mathdebate09]

Because

Recently an issue (#28253) was closed for the settings globals: true not working as expected and hence manually importing vitest functions, PR for updating the same imports in the lesson Mocking Callbacks & Components

This PR

• Import vitest functions

Issue

nil

Additional Information

nil

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[MaoShizhong]

Thanks for catching this. While you're at it, could you change that code block's indentation from 4 spaces to 2 spaces so it's consistent with the rest of the lesson (and course)?

[MaoShizhong]

🚀