fix: typo in shared_ptr chapter

[YukunJ]

Brief: Found this typo while I read through this chapter. I believe the author mean shared_from_this

https://en.cppreference.com/cpp/memory/enable_shared_from_this/shared_from_this

Exceptions
If shared_from_this is called on an object that is not previously shared by std::shared_ptr, std::bad_weak_ptr is thrown by the std::shared_ptr constructor.

@Charliechen114514

[Charliechen114514]

您好！这里非常感谢您的修正！

我重新检查了原文上下文，这里的修改是正确的。这条 warning 具体讨论的是“对象尚未被 std::shared_ptr 管理时调用会出错”的行为，因此主语应当是 shared_from_this()，而不是 enable_shared_from_this 本身。

这是我编写时的疏忽，可能给您和其他读者造成了一些困惑，对此表示非常抱歉。由于一些个人原因，我暂时没办法立刻将您的贡献同步到网站中；我计划在 6 月 7 日单独提交一个 PR 来完成网站内容同步。

最后，再次感谢您的帮助！

Thank you very much for the correction!

I rechecked the surrounding context, and this change is correct. The warning is specifically about the behavior of calling shared_from_this() when the object is not yet managed by a std::shared_ptr, so the subject here should be shared_from_this() rather than enable_shared_from_this itself.

This was an oversight on my part when writing the chapter, and I apologize if it caused any confusion for you or other readers. For some personal reasons, I am not able to sync your contribution to the website immediately. I plan to submit a separate PR on June 7 to update the website content accordingly.

Thanks again for your help!