[BUG]: Unexpected behavior assigning Python callback to C++ class

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What version (or hash if on master) of pybind11 are you using?

741d86f2e3527b667ba85d273a5eea19a0978ef5

Problem description

I'm trying to store a Python callback within a C++ object so that it can be invoked later but am noticing that the containing class is not properly destroyed on cleanup. The destructor for Container is never run, but only when the Python callback object is copied into the container. Using a reference or pointer member variable for the Python callback object appears to avoid this issue,

Reproducible example code

#include <pybind11/pybind11.h>
#include <pybind11/stl.h>
#include <pybind11/functional.h>

#include <iostream>

using Callback = std::function<void(int)>;

class Container {
public:
    Container(Callback& cb) : mCallback(cb)
    {
        std::cout << "Container::Container()" << std::endl;
    }
    ~Container()
    {
        std::cout << "Container::~Container()" << std::endl;
    }
private:
    Callback mCallback;
};

PYBIND11_MODULE(container, m) {
    pybind11::class_<Container>(m, "Container")
		.def(pybind11::init<Callback&>());
}

import container

def cb():
    pass

c = container.Container(cb)

The following works correctly, Container::~Container() is run

#include <pybind11/pybind11.h>
#include <pybind11/stl.h>
#include <pybind11/functional.h>

#include <iostream>

using Callback = std::function<void(int)>;

class Container {
public:
    Container(Callback& cb) : mCallback(cb)
    {
        std::cout << "Container::Container()" << std::endl;
    }
    ~Container()
    {
        std::cout << "Container::~Container()" << std::endl;
    }
private:
    Callback& mCallback;
};

PYBIND11_MODULE(container, m) {
    pybind11::class_<Container>(m, "Container")
		.def(pybind11::init<Callback&>());
}

Is this a regression? Put the last known working version here if it is.

Not a regression

The issue names no repository files or tests. Start by running the provided C++/Python reproducer and tracing the pybind11 callback conversion and object-lifetime path. Done means identifying why copying the callback prevents Container destruction and adding a regression check that confirms cleanup occurs.