Update the 8.11 to 8.12 update documentation to use gitlab-shell 3.5.0

Signed-off-by: Rémy Coutable <remy@rymai.me>

doc/update/8.11-to-8.12.md

@@ -70,7 +70,7 @@ sudo -u git -H git checkout 8-12-stable-ee
 ```bash
 cd /home/git/gitlab-shell
 sudo -u git -H git fetch --all --tags
-sudo -u git -H git checkout v3.4.0
+sudo -u git -H git checkout v3.5.0
 ```
 
 ### 6. Update gitlab-workhorse