fix(backend): Allow null for period_end in billing subscription item webhook (#7699)

Author: jacekradko

.changeset/quiet-doors-wave.md

@@ -0,0 +1,5 @@
+---
+'@clerk/backend': patch
+---
+
+Allow `null` for `period_end` in `BillingSubscriptionItemWebhookEventJSON`

packages/backend/src/api/resources/JSON.ts

@@ -907,7 +907,7 @@ export interface BillingSubscriptionItemWebhookEventJSON extends ClerkResourceJS
   proration_date: string;
   plan_period: 'month' | 'annual';
   period_start: number;
-  period_end?: number;
+  period_end: number | null;
   canceled_at?: number;
   past_due_at?: number;
   lifetime_paid: number;