Merge branch 'update-gitlab-shell' into 'master'

Update GitLab Shell to v12.1.0

See merge request gitlab-org/gitlab!29167

GITLAB_SHELL_VERSION

-12.0.0
+12.1.0

changelogs/unreleased/update-gitlab-shell.yml

+---
+title: Update GitLab Shell to v12.1.0
+merge_request: 29167
+author:
+type: other