GitLab

1. PrepareRefund: block refund on provider instance lookup failure
   instead of silently skipping permission check (medium severity)

2. UpdateProviderInstance: allow enabling refund_enabled and
   allow_user_refund in the same request by checking req.RefundEnabled
   value before falling back to DB read

3. ExecuteRefund: only revoke subscription on ErrAdjustWouldExpire,
   abort on other errors (DB failure, not found) instead of
   unconditionally revoking