fix disabled behaviour of start time button

assets/javascripts/discourse/components/modal/next-session-scheduled.hbs

@@ -14,7 +14,7 @@
       @action={{action "submit"}}
       class="btn-primary"
       @label="admin.wizard.after_time_modal.done"
-      disabled={{this.submitDisabled}}
+      @disabled={{this.submitDisabled}}
     />
   </div>
 </DModal>