Merge branch 'update-gitlab-shell-version-in-doc' into 'master'

Update gitlab-shell version to 3.2.1 in the 8.9->8.10 update guide

## What does this MR do?

Update gitlab-shell version to 3.2.1 in the 8.9->8.10 update guide (missing from gitlab-org/gitlab-ce!5509).

See merge request !5516

doc/update/8.9-to-8.10.md

@@ -46,7 +46,7 @@ sudo -u git -H git checkout 8-10-stable-ee
 ```bash
 cd /home/git/gitlab-shell
 sudo -u git -H git fetch --all --tags
-sudo -u git -H git checkout v3.2.0
+sudo -u git -H git checkout v3.2.1
 ```
 
 ### 5. Update gitlab-workhorse