fix: add non-null assertion on listener.mock.calls[0] (TS strict mode)

Lines 28 and 40 access mock.calls[0] which is possibly undefined under
strict TypeScript. Adding ! to satisfy TS2532.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

src/__tests__/analytics.test.ts

@@ -25,7 +25,7 @@ describe("analytics", () => {
       window.addEventListener(ANALYTICS_EVENTS.BOOKING_STEP_SERVICE, listener);
       fireAnalyticsEvent(ANALYTICS_EVENTS.BOOKING_STEP_SERVICE, { step: "service", flow: "public" });
       expect(listener).toHaveBeenCalledTimes(1);
-      const event = listener.mock.calls[0][0] as CustomEvent;
+      const event = listener.mock.calls[0]![0] as CustomEvent;
       expect(event.type).toBe("booking_step_service");
       expect(event.detail.step).toBe("service");
       expect(event.detail.flow).toBe("public");
@@ -37,7 +37,7 @@ describe("analytics", () => {
       const listener = vi.fn();
       window.addEventListener(ANALYTICS_EVENTS.BOOKING_CONFIRMED, listener);
       fireAnalyticsEvent(ANALYTICS_EVENTS.BOOKING_CONFIRMED, { step: "confirmed", flow: "public" });
-      const event = listener.mock.calls[0][0] as CustomEvent;
+      const event = listener.mock.calls[0]![0] as CustomEvent;
       expect(event.detail.timestamp).toBeTruthy();
       expect(new Date(event.detail.timestamp as string)).toBeInstanceOf(Date);
       window.removeEventListener(ANALYTICS_EVENTS.BOOKING_CONFIRMED, listener);