Self-Review Checklist:

- [x] I've reviewed my own diff for quality, security, and reliability
- [ ] Unsafe blocks (if any) have justifying comments
- [x] The content is consistent with the [UI/UX
checklist](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist)
- [ ] Tests cover the new/changed behavior
- [x] Performance impact has been considered and is acceptable

Follow up of #57312. Hides the scrollbar (which does not do anything)
when markdown code blocks are wrapped.

Release Notes:

- Fixed the scrollbar on wrapped code blocks in the agent chat.

(As far as I can see the wrap button only exists in the agent chat and
not regular markdown previews.)

---------

Co-authored-by: MrSubidubi <finn@zed.dev>