### Godot version

4.1

### System information

Windows 10.0.19045 - Vulkan (Forward+) - dedicated NVIDIA GeForce GTX 1060 (NVIDIA; 30.0.15.1403) - Intel(R) Core(TM) i7-7700HQ CPU @ 2.80GHz (8 Threads)

### Issue description


https://github.com/godotengine/godot/assets/2223172/3c8ee782-9d5f-42e3-a70f-d2aa59a233dd

We correctly clamp the size to 16x16 everywhere except here (probably).

### Steps to reproduce

1. Add a class with custom icon, e.g.
```GDScript
@icon("res://icon.svg")
extends Node
class_name Icon
```
2. Add it to scene
3. Open Script Editor and drag the node to script editor

### Minimal reproduction project

N/A
ERR_FAIL_COND(!item);
	NodePath np = item->get_metadata(0);
	if (!has_node(np)) {
		return;
	}
	Node *n = get_node(np);
	if (!n) {
		return;
	}
	if (editor_selection->is_selected(n)) {
		if (!item->is_selected(0)) {
			item->select(0);
		}
	} else {
		if (item->is_selected(0)) {
			TreeItem *previous_cursor_item = tree->get_selected();
			item->deselect(0);
			previous_cursor_item->set_as_cursor(0);
		}
	}
	TreeItem *c = item->get_first_child();
	while (c) {
		_update_selection(c);
		c = c->get_next();
	}
}
void SceneTreeEditor::_selection_changed() {