### Godot version

4.0 beta 10

### System information

Windows 11 Vulkan

### Issue description

Looked through the issues list, but couldn't find something like this, sorry in advance if this has already been reported.

There is a few cases (in the pictures below) where list of Actions in Input Map may not always show a scrollbar even if the actions list overflows (I imagine this could also happen for the widget that Input Map uses).

![image](https://user-images.githubusercontent.com/39958198/210003566-cf60dbaf-921f-485b-b0a9-51ffc28d0244.png)

![New Bitmap image](https://user-images.githubusercontent.com/39958198/210004079-8eb2e6a1-0cf5-4a7c-8905-a4e3cfd0ec5d.png)

![image](https://user-images.githubusercontent.com/39958198/210004165-a6b6790b-248a-4f68-b4d0-b44b25afdf4f.png)

![image](https://user-images.githubusercontent.com/39958198/210004537-aca52194-a464-48b9-b818-24782706de45.png)


### Steps to reproduce

The pictures are clearer than anything I could write here: "a picture is worth 1000 words"

### Minimal reproduction project

N/A
if (select_mode == SELECT_MULTI) {
		if (!p_item->cells[p_column].selectable) {
			return;
		}
		p_item->cells.write[p_column].selected = true;
		
		selected_col = p_column;
		if (!selected_item) {
			selected_item = p_item;
		}
	} else {
		select_single_item(p_item, root, p_column);
	}
	queue_redraw();
}
void Tree::item_deselected(int p_column, TreeItem *p_item) {
	if (selected_item == p_item) {
		selected_item = nullptr;
		if (selected_col == p_column) {
			selected_col = -1;
		}
	}
	if (select_mode == SELECT_MULTI || select_mode == SELECT_SINGLE) {
		p_item->cells.write[p_column].selected = false;
	}
	queue_redraw();
}
void Tree::set_select_mode(SelectMode p_mode) {