### 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
next = _n;
			} else {
				break;
			}
		}
		if (next == selected_item) {
			return;
		}
		if (select_mode == SELECT_MULTI) {
			selected_item = next;
			emit_signal(SNAME("cell_selected"));
			queue_redraw();
		} else {
			while (next && !next->cells[selected_col].selectable) {
				next = next->get_next_visible();
			}
			if (!next) {
				return; 
			}
			next->select(selected_col);
		}
		ensure_cursor_is_visible();
	} else if (p_event->is_action("ui_page_up", true) && p_event->is_pressed()) {
		if (!cursor_can_exit_tree) {
			accept_event();
		}
		TreeItem *prev = nullptr;
		if (!selected_item) {
			return;
		}