### 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
RenderingServer::get_singleton()->canvas_item_add_rect(ci, Rect2(r.position.x, r.position.y, r.size.x, 1), theme_cache.drop_position_color);
					}
					if (drop_mode_section == 0) {
						
						RenderingServer::get_singleton()->canvas_item_add_rect(ci, Rect2(r.position.x, r.position.y, 1, r.size.y), theme_cache.drop_position_color);
						RenderingServer::get_singleton()->canvas_item_add_rect(ci, Rect2(r.position.x + r.size.x - 1, r.position.y, 1, r.size.y), theme_cache.drop_position_color);
					}
					if (drop_mode_section == 0 || (drop_mode_section == 1 && (!p_item->get_first_child() || p_item->is_collapsed()))) {
						
						RenderingServer::get_singleton()->canvas_item_add_rect(ci, Rect2(r.position.x, r.position.y + r.size.y, r.size.x, 1), theme_cache.drop_position_color);
					}
				} else if (drop_mode_over == p_item->get_parent()) {
					if (drop_mode_section == 1 && !p_item->get_prev() ) { 
						
						RenderingServer::get_singleton()->canvas_item_add_rect(ci, Rect2(r.position.x, r.position.y, r.size.x, 1), theme_cache.drop_position_color);
					}
				}
			}
			Color col;
			if (p_item->cells[i].custom_color) {
				col = p_item->cells[i].color;
			} else {
				col = p_item->cells[i].selected ? theme_cache.font_selected_color : theme_cache.font_color;
			}
			Color font_outline_color = theme_cache.font_outline_color;
			int outline_size = theme_cache.font_outline_size;
			Color icon_col = p_item->cells[i].icon_color;
			if (p_item->cells[i].dirty) {
				const_cast<Tree *>(this)->update_item_cell(p_item, i);