### 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
TreeItem *s = tree->get_selected();
	ERR_FAIL_COND(!s);
	NodePath np = s->get_metadata(0);
	Node *n = get_node(np);
	if (n == selected) {
		return;
	}
	selected = get_node(np);
	blocked++;
	emit_signal(SNAME("node_selected"));
	blocked--;
}
void SceneTreeEditor::_deselect_items() {
	// Clear currently selected items in scene tree dock.
	if (editor_selection) {
		editor_selection->clear();
		emit_signal(SNAME("node_changed"));
	}
}
void SceneTreeEditor::_cell_multi_selected(Object *p_object, int p_cell, bool p_selected) {