Bound C++ object contains "garbage" after being copied in Python

Issue description

This is caused because this (in bound object) becomes an invalid pointer after copying the object in Python using copy.copy.

Reproducible example code

#include <pybind11/pybind11.h>
#include <memory>
#include <iostream>

namespace py = pybind11;

class CopyTest {
public:
    CopyTest(size_t number) : number(number) {
        std::cerr << "[CONSTRUCTOR of CopyTest at " << this << "; number = " << this->number << "]\n";
    }

    ~CopyTest() {
        std::cerr << "[DESTRUCTOR of CopyTest at " << this << "; number = " << this->number << "]\n";
    }

    CopyTest() = delete;
    CopyTest(CopyTest const&) = delete;

    size_t get_number() const { return number; }
    size_t get_memory_location() const { return reinterpret_cast<size_t>(this); }

protected:
    size_t number;
};

std::shared_ptr<CopyTest> create_copy_test(size_t number) {
    return std::make_shared<CopyTest>(number);
}

PYBIND11_MODULE(_pb11pg, m) {
    m.doc() = "pybind11 testing module";

    py::class_<CopyTest, std::shared_ptr<CopyTest>>(m, "CopyTest")
        .def_property_readonly("number", &CopyTest::get_number)
        .def_property_readonly("memory_location", &CopyTest::get_memory_location);

    m.def("create_copy_test", &create_copy_test);
}

def test_copy_error():
    import _pb11pg
    x = _pb11pg.create_copy_test(424242)

    memory_location = x.memory_location
    assert x.number == 424242

    import copy
    x_copy = copy.copy(x)

    copy_memory_location = x_copy.memory_location
    assert x_copy.number == 424242
    assert copy_memory_location == memory_location

Note that the copied object now contains "garbage":

>       assert x_copy.number == 424242
E       assert 287762808833 == 424242
E        +  where 287762808833 = <_pb11pg.CopyTest object at 0x0000012AAAFE7570>.number

and the this pointer is changed:

>       assert copy_memory_location == memory_location
E       assert 1663910680432 == 1663870278992

I've noticed that the constructor and destructor are called only once, and no copy-constructor or default-constructor are called, as I've "removed" them with = delete.

Start by building the supplied C++ binding and running the provided Python test_copy_error reproduction with copy.copy. Trace pybind11's handling of copying bound objects and their this pointers. Done means the copied object preserves the original memory location and number value without invalid object state.