[3.14] bpo-45210: Document that error indicator may be set in tp_dealloc (GH-28358) (#135298)

bpo-45210: Document that error indicator may be set in tp_dealloc (GH-28358)
(cherry picked from commit 8441b263af964f353bf02d56c32a4fc547cdc330)

Signed-off-by: Edward Z. Yang <ezyang@fb.com>
Signed-off-by: Edward Z. Yang <ezyang@meta.com>
Co-authored-by: Edward Z. Yang <ezyang@mit.edu>
Co-authored-by: Victor Stinner <vstinner@python.org>