When a new promotion with 2.5m new promo codes was created, it just generated about 250k promo codes and then stopped.

The PromotionBatch screen this error: Errored: #<ActiveRecord::RecordInvalid: Validation failed: Value has already been taken>
It seems that when the PromotionCode creation fails, it raises an exception that stops the worker.

I would like to propose changing this behavior and rescuing the exception inside the loop, so we can skip the failed code creation and continue to the next one.

Solidus Version:
All solidus version

To Reproduce
Create a promotion with 2.5M code

Current behavior
The Spree::PromotionCode::BatchBuilder worker fails with ActiveRecord::RecordInvalid: Validation failed: Value has already been taken without completing the promotion codes generation.

Expected behavior
The Spree::PromotionCode::BatchBuilder worker generates all the PromotionCodes.