文件名清理改为固定的 Windows 非法字符集，Linux CI 现在也会将 : 替换为 -。

清除了 DOCX 测试的空引用警告，以及 3 处 xUnit Assert.Single 分析器警告。

tests/Jiaowu.Api.Tests/CourseSelectionsControllerTests.cs

@@ -110,12 +110,14 @@ public sealed class CourseSelectionsControllerTests
             .OrderBy(x => x.UserId)
             .ToListAsync();
         Assert.Equal(2, resultNotifications.Count);
-        var selectedNotification = Assert.Single(resultNotifications
-            .Where(x => x.UserId == data.EnrolledUserId));
+        var selectedNotification = Assert.Single(
+            resultNotifications,
+            x => x.UserId == data.EnrolledUserId);
         Assert.Contains("最终选中 1 门", selectedNotification.Content);
         Assert.Contains("《程序设计基础》", selectedNotification.Content);
-        var waitlistNotification = Assert.Single(resultNotifications
-            .Where(x => x.UserId == data.FirstWaiterUserId));
+        var waitlistNotification = Assert.Single(
+            resultNotifications,
+            x => x.UserId == data.FirstWaiterUserId);
         Assert.Contains("本轮未选中课程", waitlistNotification.Content);
         Assert.Contains("候补未成功 1 门", waitlistNotification.Content);
         Assert.Equal(NotificationCategory.CourseSelection, waitlistNotification.Category);