Rounded window corners obscure guest's screen content

On MacOS 26, the rounded corners on the window of a VM obscure some pixels from the guest's screen, which can be problematic if you needed to be able to see them.

Screenshot of lower left corner of window:

Note that the `n` in the corner is partly obscured and nearly unreadable. In some situations it might be important to be able to read that character clearly.

**Configuration**
* UTM Version: 5.0.2 beta, also 4.7.5
* macOS Version: Tahoe 26.4
* Mac Chip (Intel, M1, ...): M3

**Debug log**

[debug.log.zip](https://github.com/user-attachments/files/26294037/debug.log.zip)

**Upload VM**

[config.plist.zip](https://github.com/user-attachments/files/26294032/config.plist.zip)