Add a close button to the restart-required notification

Fixes #4392

packages/node_modules/@node-red/editor-client/src/js/red.js

@@ -498,6 +498,15 @@ var RED = (function() {
                             ]
                         }
                     }
+                } else if (notificationId === 'restart-required') {
+                    options.buttons = [
+                        {
+                            text: RED._("common.label.close"),
+                            click: function() {
+                                persistentNotifications[notificationId].hideNotification();
+                            }
+                        }
+                    ]
                 }
                 if (!persistentNotifications.hasOwnProperty(notificationId)) {
                     persistentNotifications[notificationId] = RED.notify(text,options);