修复MySQL问题

src/Jiaowu.Api/Infrastructure/Exams/MakeupExamArrangementService.cs

@@ -225,11 +225,13 @@ public sealed class MakeupExamArrangementService(AppDbContext db)
         foreach (var id in dbBusyIds) busyTeacherIds.Add(id);
         foreach (var id in excludeTeacherIds) busyTeacherIds.Add(id);
 
-        return await db.Teachers.AsNoTracking()
-            .Where(x => x.Status == TeacherStatus.Active)
-            .WhereNotIn(busyTeacherIds, x => x.Id)
-            .OrderBy(x => Guid.NewGuid())
-            .Take(needed)
+        var candidates = await InvigilatorCandidateQuery
+            .Create(db, busyTeacherIds)
             .ToListAsync(cancellationToken);
+
+        return candidates
+            .OrderBy(_ => Random.Shared.Next())
+            .Take(needed)
+            .ToList();
     }
 }