[BUG] Factory functions declared noexcept do not work with py::init() when compiling with C++17/C++20

Issue description

A modified example from the docs with noexcept factory function will not compile.

error C2027: use of undefined type 'pybind11::detail::initimpl::factory<Func,pybind11::detail::void_type (__cdecl *)(void),init::Example (int) noexcept,pybind11::detail::void_type (void)>'
        with
        [
            Func=init::Example (__cdecl *)(int) noexcept
        ]

Reproducible example code

class Example {
   private:
    Example(int) noexcept; // private constructor
   public:
    // Factory function:
    static Example create(int a) noexcept { return Example(a); }
  };

  py::class_<Example>(m, "Example")
      .def(py::init(&Example::create));

Start with the reproducible C++ example using py::init(&Example::create) and the reported C++17/C++20 compiler error. Trace the py::init factory handling for noexcept function types; done means the example compiles and works with the supported C++17 and C++20 configurations.