Merge branch 'gitlab_shell_version_update' into 'master'

Update gitlab-shell to v3.4.0

Part of Redis Sentinel support: gitlab-shell#29

See merge request !5920

GITLAB_SHELL_VERSION

-3.3.3
+3.4.0

doc/update/8.10-to-8.11.md

@@ -46,7 +46,7 @@ sudo -u git -H git checkout 8-11-stable-ee
 ```bash
 cd /home/git/gitlab-shell
 sudo -u git -H git fetch --all --tags
-sudo -u git -H git checkout v3.3.3
+sudo -u git -H git checkout v3.4.0
 ```
 ### 5. Update gitlab-workhorse