Increase calendar polling rate to 30 s

aleksis/core/frontend/components/calendar/Calendar.vue

@@ -358,7 +358,7 @@ export default {
 
         this.fetchMoreInterval = setInterval(() => {
           this.fetchMoreCalendarEvents(extendedStart, extendedEnd);
-        }, 5000);
+        }, 30000);
 
         this.fetchedDateRanges.push({ start: extendedStart, end: extendedEnd });
       } else {
@@ -366,7 +366,7 @@ export default {
 
         this.fetchMoreInterval = setInterval(() => {
           this.fetchMoreCalendarEvents(extendedStart, extendedEnd);
-        }, 5000);
+        }, 30000);
       }
     },
   },