### 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
if (hide_root && !root->get_next_visible()) {
			return;
		}
		if (k->get_unicode() > 0) {
			_do_incr_search(String::chr(k->get_unicode()));
			accept_event();
			return;
		} else {
			if (k->get_keycode() != Key::SHIFT) {
				last_keypress = 0;
			}
		}
	}
	Ref<InputEventMouseMotion> mm = p_event;
	if (mm.is_valid()) {
		Ref<StyleBox> bg = theme_cache.panel_style;
		bool rtl = is_layout_rtl();
		Point2 pos = mm->get_position();
		if (rtl) {
			pos.x = get_size().width - pos.x;
		}
		pos -= theme_cache.panel_style->get_offset();
		Cache::ClickType old_hover = cache.hover_type;
		int old_index = cache.hover_index;
		cache.hover_type = Cache::CLICK_NONE;
		cache.hover_index = 0;
		if (show_column_titles) {
			pos.y -= _get_title_button_height();
			if (pos.y < 0) {
				pos.x += theme_cache.offset.x;