### Godot version

4.1.dev (dc625bcbfc5b587ba8867481ee7a1f6a567c25d0)

### System information

Mageia 9, Linux

### Issue description

When importing a project in current `master`, the following error is raised for each asset that gets imported:
```
Attempting to parent and popup a dialog that already has a parent.
```

It seems to be raised once per asset, caused by the progress dialog.

CC @bruvzg

### Steps to reproduce

- Import a new project in Godot that contains importable assets, e.g. https://github.com/RPicster/godot4-demo-desert-light

### Minimal reproduction project

See above.
Popup::_update_theme_item_cache();
	theme_cache.panel_style = get_theme_stylebox(SNAME("panel"));
}
void PopupPanel::_notification(int p_what) {
	switch (p_what) {
		case NOTIFICATION_READY:
		case NOTIFICATION_THEME_CHANGED: {
			panel->add_theme_style_override("panel", theme_cache.panel_style);
			_update_child_rects();
		} break;
		case NOTIFICATION_WM_SIZE_CHANGED: {
			_update_child_rects();
		} break;
	}
}
PopupPanel::PopupPanel() {
	panel = memnew(Panel);
	add_child(panel, false, INTERNAL_MODE_FRONT);
}