Testing Practice: Add link to Jest Experimental ESM Support

[shonebinu]

Because

Jest has experimental support for ES modules. I've done my Testing Practice Project with it. https://github.com/shonebinu/testing-practice

This PR

• Adds a link to Jest ESM documentation.

Issue

Closes #XXXXX

Additional Information

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[MaoShizhong]

Going to close this one precisely because the ESM support is experimental. Since it's unstable and subject to change (because it's based around an experimental Node API), I don't think it's sensible to include that in the curriculum yet. If an when it's able to implement stable support, we can then change our lesson material to reflect that.

[shonebinu]

I see.
I included it because, I saw it as the first solution for this problem in StackOverflow. https://stackoverflow.com/questions/68956636/how-to-use-esm-tests-with-jest

But I can understand your judgement, thanks for the feedback!