### 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
ERR_FAIL_COND_V(blocked > 0, nullptr);
	TreeItem *ti = nullptr;
	if (p_parent) {
		ERR_FAIL_COND_V_MSG(p_parent->tree != this, nullptr, "A different tree owns the given parent");
		ti = p_parent->create_child(p_idx);
	} else {
		if (!root) {
			
			ti = memnew(TreeItem(this));
			ERR_FAIL_COND_V(!ti, nullptr);
			ti->cells.resize(columns.size());
			ti->is_root = true;
			root = ti;
		} else {
			
			ti = create_item(root, p_idx);
		}
	}
	return ti;
}
TreeItem *Tree::get_root() const {
	return root;
}
TreeItem *Tree::get_last_item() const {