### 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 *ti = memnew(TreeItem(tree));
	if (tree) {
		ti->cells.resize(tree->columns.size());
		tree->queue_redraw();
	}
	TreeItem *l_prev = nullptr;
	TreeItem *c = first_child;
	int idx = 0;
	while (c) {
		if (idx++ == p_idx) {
			c->prev = ti;
			ti->next = c;
			break;
		}
		l_prev = c;
		c = c->next;
	}
	if (l_prev) {
		l_prev->next = ti;
		ti->prev = l_prev;
		if (!children_cache.is_empty()) {
			if (ti->next) {
				children_cache.insert(p_idx, ti);
			} else {
				children_cache.append(ti);
			}
		}
	} else {