### 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
_unlink_from_tree();
	validate_cache();
	prev = nullptr;
	clear_children();
	_change_tree(nullptr);
}
void Tree::_update_theme_item_cache() {
	Control::_update_theme_item_cache();
	theme_cache.panel_style = get_theme_stylebox(SNAME("panel"));
	theme_cache.focus_style = get_theme_stylebox(SNAME("focus"));
	theme_cache.font = get_theme_font(SNAME("font"));
	theme_cache.font_size = get_theme_font_size(SNAME("font_size"));
	theme_cache.tb_font = get_theme_font(SNAME("title_button_font"));
	theme_cache.tb_font_size = get_theme_font_size(SNAME("title_button_font_size"));
	theme_cache.selected = get_theme_stylebox(SNAME("selected"));
	theme_cache.selected_focus = get_theme_stylebox(SNAME("selected_focus"));
	theme_cache.cursor = get_theme_stylebox(SNAME("cursor"));
	theme_cache.cursor_unfocus = get_theme_stylebox(SNAME("cursor_unfocused"));
	theme_cache.button_pressed = get_theme_stylebox(SNAME("button_pressed"));
	theme_cache.checked = get_theme_icon(SNAME("checked"));
	theme_cache.unchecked = get_theme_icon(SNAME("unchecked"));
	theme_cache.indeterminate = get_theme_icon(SNAME("indeterminate"));
	theme_cache.arrow = get_theme_icon(SNAME("arrow"));
	theme_cache.arrow_collapsed = get_theme_icon(SNAME("arrow_collapsed"));
	theme_cache.arrow_collapsed_mirrored = get_theme_icon(SNAME("arrow_collapsed_mirrored"));
	theme_cache.select_arrow = get_theme_icon(SNAME("select_arrow"));
	theme_cache.updown = get_theme_icon(SNAME("updown"));
	theme_cache.custom_button = get_theme_stylebox(SNAME("custom_button"));
	theme_cache.custom_button_hover = get_theme_stylebox(SNAME("custom_button_hover"));