Fix binding of default value in EditorSpatialGizmoPlugin::get_material()

It was commented for some reason I can't remember.

(cherry picked from commit e6949dae724b923227bdd61f8732667d997686a7)

doc/classes/EditorSpatialGizmoPlugin.xml

@@ -122,7 +122,7 @@
 			</return>
 			<argument index="0" name="name" type="String">
 			</argument>
-			<argument index="1" name="gizmo" type="EditorSpatialGizmo">
+			<argument index="1" name="gizmo" type="EditorSpatialGizmo" default="null">
 			</argument>
 			<description>
 				Gets material from the internal list of materials. If an [EditorSpatialGizmo] is provided, it will try to get the corresponding variant (selected and/or editable).

editor/plugins/spatial_editor_plugin.cpp

@@ -6848,7 +6848,7 @@ void EditorSpatialGizmoPlugin::_bind_methods() {
 	ClassDB::bind_method(D_METHOD("create_handle_material", "name", "billboard"), &EditorSpatialGizmoPlugin::create_handle_material, DEFVAL(false));
 	ClassDB::bind_method(D_METHOD("add_material", "name", "material"), &EditorSpatialGizmoPlugin::add_material);
 
-	ClassDB::bind_method(D_METHOD("get_material", "name", "gizmo"), &EditorSpatialGizmoPlugin::get_material); //, DEFVAL(Ref<EditorSpatialGizmo>()));
+	ClassDB::bind_method(D_METHOD("get_material", "name", "gizmo"), &EditorSpatialGizmoPlugin::get_material, DEFVAL(Ref<EditorSpatialGizmo>()));
 
 	BIND_VMETHOD(MethodInfo(Variant::STRING, "get_name"));
 	BIND_VMETHOD(MethodInfo(Variant::INT, "get_priority"));