[TreeDataGrid] Can't select the bottom row

[clintsinger]

Describe the bug

When the horizontal scrollbar is visible the bottom row of the TreeDataGrid isn't selectable.

To Reproduce

1. Create TreeDataGrid and add enough data to show scrollbars
2. Click on the last row
3. Observe that the horizontal scrollbar blocks selecting the last row
4. Modify data / UI so that the horizontal scrollbar disappears
5. Observe that you can select the bottom row

Expected behavior

You should be able to select the bottom row even if the scrollbar is visible.

Avalonia version

Avalonia: 11.3.0, Avalonia.Controls.TreeDataGrid: 11.1.1

OS

No response

Additional context

No response