Add NoShippingPostCampaignCheckoutViewController to payment methods assert

[ifosli]

📲 What

Our PledgePaymentMethodsViewController has an assert to make sure it's only presented in the pledge flow. The no shipping late pledge flow was missing from the assert, so I'm adding it in.

Note: Since asserts like this default to true in production, there's no impact on our current release.

✅ Acceptance criteria

• The add payment methods sheet gets presented without crashing the app in debug builds with the "no shipping at pledge" and the "post campaign pledging enabled" flags on.