[3.14] gh-140530: fix a reference leak in an error path for `raise exc from cause` (GH-140908) (#141282)

gh-140530: fix a reference leak in an error path for `raise exc from cause` (GH-140908)

Fix a reference leak in `raise E from T` when `T` is an exception
subtype for which `T.__new__` does not return an exception instance.
(cherry picked from commit 0c77e7c23b5c270a3142105542c56c59b59c52a0)

Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>