Remove redundant move in test

[hpkfft]

An out-of-the box build with Debian trixie (i.e., with g++ 14.2.0) gives the following warning:

warning: redundant move in return statement [-Wredundant-move]
  508 |     m.def("test_type_object_t", [](nb::type_object_t<Struct> h) -> nb::object { return std::move(h); });
      |                                                                                        ~~~~~~~~~^~~

Since the return expression is move-eligible, the move constructor is selected without the std::move.

[wjakob]

So AFAIK I added this std::move() because of a compiler warning saying that I needed an explicit move to avoid using a converting constructor. But I can't repro it anymore. Will merge this for now.