[3.13] Docs: Fix specifications of `gcvisitobjects_t` (GH-132433) (#132441)

Docs: Fix specifications of `gcvisitobjects_t` (GH-132433)

`gcvisitobjects_t` callbacks should return 1 for the iteration to continue instead of 0.
(cherry picked from commit 1e5798e37255e921beae2aaa8329d5c48a2ef230)

Co-authored-by: da-woods <dw-git@d-woods.co.uk>