Drupal 9 - change the temporary file directory path without the UI
Example with Drush
drush config:set system.file path.temporary /tmp -y
Example with settings.php
If done through settings.php it will no longer be changeable via either the interface or Drush.
Drupal 8.8+
See the change record.
$settings['file_temp_path'] = '/tmp';
Drupal 8.7 and below
$config['system.file']['path']['temporary'] = '/tmp';
