Fix checkout.session.async_payments_* triggers

[ahlee-stripe]

Reviewers

r? @stripe/developer-products
cc @stripe/dev-platform

Summary

• Fix small string/int conversion error in pkg/fixtures
• Update checkout.session.async_payments_failed and checkout.session.async_payments_succeeded to set "setup_future_usage": "off_session". This is required when creating a checkout session in payment mode for BACS direct (https://stripe.com/docs/payments/bacs-debit/accept-a-payment#create-session)

Testing

Switched to a UK based stripe account. Ran $ stripe-dev trigger checkout.session.async_payment_succeeded and $ stripe-dev trigger checkout.session.async_payment_failed while using stripe listen. Confirmed that all the events came through as expected.

[tomer-stripe]

Thanks @ahlee-stripe! This looks good. Let me see if I can test out the fixtures version error later, that came up in my PR too (https://github.com/stripe/stripe-cli/pull/502/files#diff-133d387253cca3c9f0d5be8b5c845987) and I'm wondering if there's a difference (or if we care) about rendering it as a decimal.

[ahlee-stripe]

@tomer-stripe If you want I can pull out the fixtures error fix so more testing can happen on it

[tomer-stripe]

@ahlee-stripe yea that would be great, ty!

[ahlee-stripe]

@tomer-stripe Done! Removed the conversion fix.