### 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 (p_item->cells[i].custom_draw_obj.is_valid()) {
						Object *cdo = ObjectDB::get_instance(p_item->cells[i].custom_draw_obj);
						if (cdo) {
							cdo->call(p_item->cells[i].custom_draw_callback, p_item, Rect2(item_rect));
						}
					}
					if (!p_item->cells[i].editable) {
						draw_item_rect(p_item->cells.write[i], item_rect, col, icon_col, outline_size, font_outline_color);
						break;
					}
					Ref<Texture2D> downarrow = theme_cache.select_arrow;
					Rect2i ir = item_rect;
					Point2i arrow_pos = item_rect.position;
					arrow_pos.x += item_rect.size.x - downarrow->get_width();
					arrow_pos.y += Math::floor(((item_rect.size.y - downarrow->get_height())) / 2.0);
					ir.size.width -= downarrow->get_width();
					if (p_item->cells[i].custom_button) {
						if (cache.hover_item == p_item && cache.hover_cell == i) {
							if (Input::get_singleton()->is_mouse_button_pressed(MouseButton::LEFT)) {
								draw_style_box(theme_cache.custom_button_pressed, ir);
							} else {
								draw_style_box(theme_cache.custom_button_hover, ir);
								col = theme_cache.custom_button_font_highlight;
							}
						} else {
							draw_style_box(theme_cache.custom_button, ir);
						}
						ir.size -= theme_cache.custom_button->get_minimum_size();
						ir.position += theme_cache.custom_button->get_offset();
					}