### 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
TreeItem *last = root;
	while (last) {
		if (last->next) {
			last = last->next;
		} else if (last->first_child) {
			last = last->first_child;
		} else {
			break;
		}
	}
	return last;
}
void Tree::item_edited(int p_column, TreeItem *p_item, MouseButton p_custom_mouse_index) {
	edited_item = p_item;
	edited_col = p_column;
	if (p_item != nullptr && p_column >= 0 && p_column < p_item->cells.size()) {
		edited_item->cells.write[p_column].dirty = true;
	}
	emit_signal(SNAME("item_edited"));
	if (p_custom_mouse_index != MouseButton::NONE) {
		emit_signal(SNAME("custom_item_clicked"), p_custom_mouse_index);
	}
}
void Tree::item_changed(int p_column, TreeItem *p_item) {
	if (p_item != nullptr && p_column >= 0 && p_column < p_item->cells.size()) {
		p_item->cells.write[p_column].dirty = true;
	}
	queue_redraw();
}
void Tree::item_selected(int p_column, TreeItem *p_item) {