maint: secondary updates from make fetch.

* maintainer/maint.mk (git-sv-host): switch to
cgit.git.savannah.gnu.org/cgit, since https://git.savannah.gnu.org
has become unreliable, due to AI crawler bombardment.
(SV_GIT_CF, SV_GIT_GL): update.
https://lists.gnu.org/archive/html/savannah-hackers-public/2025-05/msg00040.html

* lib/INSTALL: update with make fetch.
* lib/gendocs.sh: likewise.
3 files changed