Actually, should throw an error by default

sea-orm-migration/src/lib.rs

@@ -25,6 +25,6 @@ pub trait MigrationTrait: MigrationName + Send + Sync {
 
     /// Define actions to perform when rolling back the migration
     async fn down(&self, manager: &SchemaManager) -> Result<(), DbErr> {
-        Ok(())
+        Err(DbErr::Migration("We Don't Do That Here"))
     }
 }