[applets/notifications] Improve string for when to end DND mode

Change "Until turned off" to "Until manually disabled" because "turned off"
can to some users imply turning off the computer, not the DND mode.

applets/notifications/package/contents/ui/FullRepresentation.qml

@@ -161,7 +161,7 @@ PlasmaComponents3.Page {
                             d = dndMenu.date;
                             // Just set it to one year in the future so we don't need yet another "do not disturb enabled" property
                             d.setFullYear(d.getFullYear() + 1);
-                            model.push({date: d, text: i18n("Until turned off")});
+                            model.push({date: d, text: i18n("Until manually disabled")});
 
                             return model;
                         }