MDL-84205 mod_assign: allow automatic reopen method to admin defaults.

This option was added in b7e6a176 to the module form, but without the
ability for the admin to set as the default value.

mod/assign/settings.php

@@ -239,6 +239,7 @@ if ($ADMIN->fulltree) {
 
     $options = [
         ASSIGN_ATTEMPT_REOPEN_METHOD_MANUAL => new lang_string('attemptreopenmethod_manual', 'mod_assign'),
+        ASSIGN_ATTEMPT_REOPEN_METHOD_AUTOMATIC => new lang_string('attemptreopenmethod_automatic', 'mod_assign'),
         ASSIGN_ATTEMPT_REOPEN_METHOD_UNTILPASS => new lang_string('attemptreopenmethod_untilpass', 'mod_assign'),
     ];
     $name = new lang_string('attemptreopenmethod', 'mod_assign');