[3.13] gh-140530: fix a reference leak in an error path for `raise exc from cause` (GH-140908) (#141283)

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