Fix scene tree dock icon not switching colors on theme change

This fixes the "three vertical dots" button at the right of the
scene tree dock when switching from a dark theme to a light theme
or vice versa.

editor/scene_tree_dock.cpp

@@ -1306,6 +1306,7 @@ void SceneTreeDock::_notification(int p_what) {
 			button_instance->set_icon(get_theme_icon(SNAME("Instance"), SNAME("EditorIcons")));
 			button_create_script->set_icon(get_theme_icon(SNAME("ScriptCreate"), SNAME("EditorIcons")));
 			button_detach_script->set_icon(get_theme_icon(SNAME("ScriptRemove"), SNAME("EditorIcons")));
+			button_tree_menu->set_icon(get_theme_icon(SNAME("GuiTabMenuHl"), SNAME("EditorIcons")));
 			button_2d->set_icon(get_theme_icon(SNAME("Node2D"), SNAME("EditorIcons")));
 			button_3d->set_icon(get_theme_icon(SNAME("Node3D"), SNAME("EditorIcons")));
 			button_ui->set_icon(get_theme_icon(SNAME("Control"), SNAME("EditorIcons")));