fix(backend): Declare slug property in sms.created webhook event (#4024)

Co-authored-by: Bryce Kalow <bryce@clerk.dev>

Author: tmoran-stenoa

.changeset/fair-worms-joke.md

@@ -0,0 +1,5 @@
+---
+"@clerk/backend": patch
+---
+
+Add missing `slug` property in TS type declaration for SMS webhook events

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

@@ -272,6 +272,7 @@ export interface SMSMessageJSON extends ClerkResourceJSON {
   user_id?: string;
   message: string;
   status: string;
+  slug?: string | null;
   data?: Record<string, any> | null;
   delivered_by_clerk: boolean;
 }