### 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
#include "tree.h"
#include "core/config/project_settings.h"
#include "core/input/input.h"
#include "core/math/math_funcs.h"
#include "core/os/keyboard.h"
#include "core/os/os.h"
#include "core/string/print_string.h"
#include "core/string/translation.h"
#include "scene/gui/box_container.h"
#include "scene/main/window.h"
#include <limits.h>
Size2 TreeItem::Cell::get_icon_size() const {