test: model past-due subscription in cloud e2e

Amp-Thread-ID: https://ampcode.com/threads/T-01a001d5-47e3-720d-8e82-82c45995251e
Co-authored-by: Amp <amp@ampcode.com>

Author: dante01yoon

browser_tests/tests/dialogs/creditsTile.spec.ts

@@ -88,6 +88,7 @@ const endedPersonalBillingStatus: BillingStatusResponse = {
 const pastDueBillingStatus: BillingStatusResponse = {
   ...mockBillingStatus,
   is_active: false,
+  plan_slug: 'pro-monthly',
   billing_status: 'payment_failed'
 }