Add null and default to migration

db/post_migrate/20220627084020_drop_additional_amount_available_from_ci_namespace_monthly_usages.rb

@@ -4,6 +4,6 @@ class DropAdditionalAmountAvailableFromCiNamespaceMonthlyUsages < Gitlab::Databa
   enable_lock_retries!
 
   def change
-    remove_column :ci_namespace_monthly_usages, :additional_amount_available, :integer
+    remove_column :ci_namespace_monthly_usages, :additional_amount_available, :integer, null: false, default: 0
   end
 end