docs(testing): add JSDoc typing in `jest.config.js` (#40090)
docs(testing): add JSDoc typing in `jest.config.js` (#40090)

This PR improves the Testing documentation in [Setting up Jest (with the Rust Compiler)](https://nextjs.org/docs/testing#setting-up-jest-with-the-rust-compiler). It adds JSDoc typing in `jest.config.js`.

## Documentation / Examples

- [x] Make sure the linting passes by running `pnpm lint`

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