Merge branch 'patch-7' into 'master'

This will change the update process to checkout gitlab-shell version 3.6.6 instead of 3.6.3 as currently described in the update document

See merge request !6976

doc/update/8.12-to-8.13.md

@@ -72,7 +72,7 @@ sudo -u git -H git checkout 8-13-stable-ee
 ```bash
 cd /home/git/gitlab-shell
 sudo -u git -H git fetch --all --tags
-sudo -u git -H git checkout v3.6.3
+sudo -u git -H git checkout v3.6.6
 ```
 
 ### 6. Update gitlab-workhorse