Render default contents in FullCalendar content injection functions

Changed in v6, as per https://fullcalendar.io/docs/upgrading-from-v5#content-injection

src/index.ts

@@ -40,6 +40,7 @@ const calendarOptions: CalendarOptions = {
         h('a', { href: ical_link }, ' [iCal 📅]')
       );
     }
+    return true;
   },
   eventContent: (arg: EventContentArg, h: typeof createElement) => {
     if (arg.view.type != 'resourceTimeline') {
@@ -66,6 +67,7 @@ const calendarOptions: CalendarOptions = {
         )
       );
     }
+    return true;
   },
 };