Bug with inheritance, shared_ptr holder and enable_shared_from_this

Issue description

error C2683: 'dynamic_cast': 'base' is not a polymorphic type

If base derives from std::enable_shared_from_this, pybind11 uses dynamic_cast, even if type is not polymorphic.

Reproducible example code

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

struct base : public std::enable_shared_from_this<base>
{
};

struct derived : base
{
};

void python_export(pybind11::module& m)
{
	pybind11::class_<base, std::shared_ptr<base>>(m, "Base")
		.def(pybind11::init<>())
	;

	pybind11::class_<derived, base, std::shared_ptr<derived>>(m, "Derived")
		.def(pybind11::init<>())
	;
}

Start by compiling and running the reproducible C++ example with pybind11, focusing on the shared_ptr holder and inheritance path for base and derived. Trace where enable_shared_from_this causes dynamic_cast to be used and verify the behavior for a non-polymorphic base. Done means the example compiles without C2683 while preserving the shared_ptr inheritance behavior.