2.6.0

• Add the following callbacks (Thanks @4nd2in !):
  • checkout.session.async_payment_failed
  • checkout.session.async_payment_succeeded
  • customer.subscription.paused
  • customer.subscription.pending_update_applied
  • customer.subscription.pending_update_expired
  • customer.subscription.resumed
  • invoice.deleted
  • invoice.finalization_failed
  • invoice.overdue
  • invoice.will_be_due
• Fix request handling in rack versions >= 3.1 where Request#[] is deprecated (#230). Thanks @4nd2in and
  @light-flight !
• adds testing for Ruby 3 and Rails 7
• stops testing on Ruby < 3 and Rails 5