### 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
int idx = 0;
	TreeItem *c = this;
	while (c) {
		c = c->get_prev();
		idx++;
	}
	return idx - 1;
}
#ifdef DEV_ENABLED
void TreeItem::validate_cache() const {
	if (!parent || parent->children_cache.is_empty()) {
		return;
	}
	TreeItem *scan = parent->first_child;
	int index = 0;
	while (scan) {
		DEV_ASSERT(parent->children_cache[index] == scan);
		++index;
		scan = scan->get_next();
	}
	DEV_ASSERT(index == parent->children_cache.size());
}
#endif
void TreeItem::move_before(TreeItem *p_item) {