Nu is a shell language so it should has the `terminal` icon.

Release Notes:

- N/A

<img width="241" alt="Capture d’écran 2024-02-25 à 18 49 43"
src="https://github.com/zed-industries/zed/assets/24520681/0adcd8fd-f5b0-4688-b301-5c49c376c7a0">