Fix(booking-slot): Check correct context for exit

backend/internal/ktmtrainbot/backgroundbookingjob.go

@@ -231,7 +231,7 @@ func (env *Env) startBooking(job *Booking, username string, password string, cre
 	select {
 	case page = <-pageChan:
 		log.Println("Page received.")
-	case <-getBookingSlotCtx.Done():
+	case <-timerCtx.Done():
 		log.Println("Context cancelled.")
 		browser.MustClose()
 		return false