Fix UndoRedo in Gradient editor

(cherry picked from commit a384031326b96dd1185b7ba33809660ba5551549)

editor/plugins/gradient_editor_plugin.cpp

@@ -51,7 +51,7 @@ void GradientEditor::_gradient_changed() {
 void GradientEditor::_ramp_changed() {
 	editing = true;
 	UndoRedo *undo_redo = EditorNode::get_singleton()->get_undo_redo();
-	undo_redo->create_action(TTR("Gradient Edited"));
+	undo_redo->create_action(TTR("Gradient Edited"), UndoRedo::MERGE_ENDS);
 	undo_redo->add_do_method(gradient.ptr(), "set_offsets", get_offsets());
 	undo_redo->add_do_method(gradient.ptr(), "set_colors", get_colors());
 	undo_redo->add_undo_method(gradient.ptr(), "set_offsets", gradient->get_offsets());