Handle backup creation on same domain as server (#592)

In case the webUI is hosted by the server the backup creation caused the app to navigate to the backup url which resulted in an empty page

Regression introduced with db5d3ff7c0

src/screens/settings/Backup.tsx

@@ -227,7 +227,7 @@ export function Backup() {
     return (
         <>
             <List sx={{ padding: 0 }}>
-                <ListItemLink to={requestManager.getExportBackupUrl()}>
+                <ListItemLink to={requestManager.getExportBackupUrl()} download target="_self">
                     <ListItemText
                         primary={t('settings.backup.action.create.label.title')}
                         secondary={t('settings.backup.action.create.label.description')}