GroupBox bottom border is clipped in certain situations

[MrJul]

Describe the bug

At some specific sizes, the bottom border of the GroupBox is incorrectly clipped:

To Reproduce

With WithInterFont():

<StackPanel Margin="10">
  <StackPanel.Resources>
    <!-- Problematic font sizes: 2, 5, 12, 15, 19, 22, 25, ... -->
    <x:Double x:Key="GroupBoxHeaderFontSize">19</x:Double>
  </StackPanel.Resources>
  <GroupBox Header="Border Clipping" BorderThickness="1" BorderBrush="Red" Padding="0">
    <TextBlock>Why is the bottom border being clipped?</TextBlock>
  </GroupBox>
</StackPanel>

Expected behavior

The bottom border isn't clipped.

Avalonia version

12.0.0-rc1, master

OS

No response

Additional context

No response