fix: apply and simplify jest lint rules

[ojeytonwilliams]

Checklist:

• I have read freeCodeCamp's contribution guidelines.
• My pull request has a descriptive title (not a vague title like Update index.md)

The rules weren't being applied to our tests, so I changed the override. Also, the recommended and style configurations have some nice defaults, so I think we can just use them until we feel a need to
configure them.

[huyenltnguyen]

Thanks, Oliver 👍