### Godot version

v4.0.beta.custom_build [eaf306e0b]

### System information

Windows 10

### Issue description

Selecting a `Window` node in the Editor's SceneTree results in the message
```
editor/editor_data.cpp:1058 - Parameter "p_node" is null.
```
and the Inspector shows empty content instead of the Window's properties.

I would expect, that clicking on a node in the SceneTree lets me edit the properties of the node.

Bisecting shows that this behavior got introduced in #71770

### Steps to reproduce

1. Create a Window node
2. Click on the Window node in the Editor's SceneTree

### Minimal reproduction project

N/A
#include "theme_editor_plugin.h"
#include "core/os/keyboard.h"
#include "editor/editor_file_dialog.h"
#include "editor/editor_node.h"
#include "editor/editor_resource_picker.h"
#include "editor/editor_scale.h"
#include "editor/editor_undo_redo_manager.h"
#include "editor/progress_dialog.h"
#include "scene/gui/color_picker.h"
#include "scene/gui/panel_container.h"
#include "scene/gui/split_container.h"
#include "scene/theme/theme_db.h"
void ThemeItemImportTree::_update_items_tree() {