In the `...` menu, we use `Discard...`

<img width="390" height="317" alt="SCR-20251217-kbdh"
src="https://github.com/user-attachments/assets/f88271a6-efab-48fb-bac1-2dacf4fad8f0"
/>

But in the context menu of each entry, we use "Restore..."

<img width="366" height="250" alt="SCR-20251217-kbcj"
src="https://github.com/user-attachments/assets/6c10842b-80f4-4868-a655-2703cba6bd5e"
/>

This PR just makes this more consistent, by using "Discard..." in the
second case.

Release Notes:

- Unified wording for discarding file changes in git panel