bpo-35081: Move _PyObject_GC_TRACK() to pycore_object.h by vstinner · Pull Request #10276 · python/cpython

Python.h now automatically includes pycore_object.h

Without that, at least 33 C files has to be modified to add include pycore_object.h: see my first attempt, PR #10272.

I prefer to have smaller PR, easier to review. The automatic include can be removed later.