[3.12] Docs: Fix documentation for "PyTypeObject Definition" (GH-130936) (GH-131459)

The structure definition for `PyTypeObject` is in `Include/cpython/object.h`,
not in `Include/object.h`.
(cherry picked from commit a0478c9)

Co-authored-by: Yuki Kobayashi <[email protected]>

Author: miss-islington