### 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_bg_color) {
				Rect2 r = cell_rect;
				if (i == 0) {
					r.position.x = p_draw_ofs.x;
					r.size.x = w + ofs;
				} else {
					r.position.x -= theme_cache.h_separation;
					r.size.x += theme_cache.h_separation;
				}
				if (rtl) {
					r.position.x = get_size().width - r.position.x - r.size.x;
				}
				if (p_item->cells[i].custom_bg_outline) {
					RenderingServer::get_singleton()->canvas_item_add_rect(ci, Rect2(r.position.x, r.position.y, r.size.x, 1), p_item->cells[i].bg_color);
					RenderingServer::get_singleton()->canvas_item_add_rect(ci, Rect2(r.position.x, r.position.y + r.size.y - 1, r.size.x, 1), p_item->cells[i].bg_color);
					RenderingServer::get_singleton()->canvas_item_add_rect(ci, Rect2(r.position.x, r.position.y, 1, r.size.y), p_item->cells[i].bg_color);
					RenderingServer::get_singleton()->canvas_item_add_rect(ci, Rect2(r.position.x + r.size.x - 1, r.position.y, 1, r.size.y), p_item->cells[i].bg_color);
				} else {
					RenderingServer::get_singleton()->canvas_item_add_rect(ci, r, p_item->cells[i].bg_color);
				}
			}
			if (drop_mode_flags && drop_mode_over) {
				Rect2 r = cell_rect;
				if (rtl) {
					r.position.x = get_size().width - r.position.x - r.size.x;
				}
				if (drop_mode_over == p_item) {
					if (drop_mode_section == 0 || drop_mode_section == -1) {