Quake mode has rounded corners in Windows 11

### Windows Terminal version (or Windows build number)

Windows 11 - 10.0.22000.0 | Terminal preview 1.9.1523.0

### Other Software

Windows 11 preview

### Steps to reproduce

I installed the terminal preview before updating, but I assume it'll have the same behavior whether you install before or after.

After finishing the Windows 11 upgrade, opening the terminal quake mode drop-down, the corners at the top and bottom are curved instead of filling in the full area.

I understand that this is the behavior that Windows 11 has by default for its apps, but this looks weird for the quake mode terminal.

### Expected Behavior

The quake terminal shows without rounded edges.

### Actual Behavior

The quake terminal shows with rounded edges


Reproduce the issue by opening the Windows Terminal quake mode drop-down on Windows 11 and compare its top and bottom edges with the expected full-area appearance. No source file or test is named, so trace the quake mode window styling from that entry point; done means the quake terminal displays without rounded edges.

Written by the indexing model from the issue text.