bug fixes

src/pages/exam/testExam/index.vue

 <template>
   <app-container title="模拟考试">
     <template #header-right>
-      <el-select v-model="courseId" @change="getExamList" placeholder="请选择课程">
+      <el-select v-model="courseId" @change="getExamList" placeholder="请选择课程" clearable style="width:300px">
         <el-option v-for="item in courses" :key="item.id" :label="item.course_name" :value="item.id"></el-option>
       </el-select>
     </template>