Fix: prefer .is_none() over .is(py::none()) for pybind11 (#88051)
Fixes minor perf regression I saw in #85688 and replaced throughout the code base. `obj == Py_None` is directly equivalent to is_none(). Constructing a temporary py::none() object needlessly incref/decref the refcount of py::none, this method avoids that and therefore is more efficient.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/88051
Approved by: https://github.com/albanD
