Fix misuse of PyObject_IsSubclass (#44769)
Summary:
PyObject_IsSubclass may set python live exception bit if given object is not a class. `IsNamedTuple` is currently using it incorrectly, which may trip all following python operations in debug-build python. Normal release-build python is not affected because `assert` is no-op in release-build.
Fixes https://github.com/pytorch/pytorch/issues/43577
Pull Request resolved: https://github.com/pytorch/pytorch/pull/44769
Reviewed By: jamesr66a
Differential Revision: D23725584
Pulled By: gmagogsfm
fbshipit-source-id: 2dabd4f8667a045d5bf75813500876c6fd81542b
