Improve diff stats bar (#30669)

Improve diff stats bar (#30669)

Minor tweaks:

- Remove unnecessary `item` class which was causing unwanted padding to
be added.
- Add some padding and prevent wrapping so it looks better on mobile.
- Increase width by 4px.

<img width="116" alt="Screenshot 2024-04-24 at 00 15 07"
src="https://github.com/go-gitea/gitea/assets/115237/1f1cf54c-8053-4297-b309-71d9c2ceb9ee">
<img width="441" alt="Screenshot 2024-04-24 at 00 14 57"
src="https://github.com/go-gitea/gitea/assets/115237/2f3a33dc-edad-4b97-b64c-6812aae513cb">