CavasItem's clip only mode on skewed styleboxes fails to clear.

[ThePhantomLemon]

Tested versions

• Reproducible in: 4.3.stable

System information

Godot v4.3.stable.mono - Windows 10.0.22631 - Vulkan (Forward+) - dedicated NVIDIA GeForce GTX 1660 Ti (NVIDIA; 32.0.15.6636) - AMD Ryzen 7 4800H with Radeon Graphics (16 Threads)

Issue description

As you can see, the portions of the stylebox outside the bounding box are not being cleared; artifacts of previous frames persist.

Steps to reproduce

Create a panel with a flat stylebox.
Skew the stylebox.
Put any visible child inside the panel.

Minimal reproduction project (MRP)

panel.zip

[ThePhantomLemon]

Just noticed that this is also the case with expanded margins in general, not just skewed boxes.