fix: todo 내 user cascade all 삭제

Author: KSH0326

src/main/java/com/back/domain/study/todo/entity/Todo.java

@@ -15,7 +15,7 @@
 @Getter
 @NoArgsConstructor
 public class Todo extends BaseEntity {
-    @ManyToOne(fetch = FetchType.LAZY, cascade = CascadeType.ALL)
+    @ManyToOne(fetch = FetchType.LAZY)
     @JoinColumn(name = "user_id")
     private User user;