[3.12] gh-120937: Reference weakref from the `__del__` documentation (GH-120940) (#121062)

gh-120937: Reference weakref from the `__del__` documentation (GH-120940)
(cherry picked from commit 1c13b29d54ad6d7c9e030227d575ad7d21b4054f)

Co-authored-by: chaen <christophe.haen@cern.ch>
Co-authored-by: Hugo van Kemenade <1324225+hugovk@users.noreply.github.com>