fix(StudyCoursePage): 修复检查任务列表长度时的引用错误

@@ -415,7 +415,7 @@ const handleCheckInSubmit = async () => {
 };
 
 const goToCheckin = () => {
-    if(!task_list.length) {
+    if(!task_list.value.length) {
         showToast('暂无打卡任务');
         return;
     }