Merge branch 'ensure-auto-merge-is-set-in-merge-train-validations' into 'master'

Ensure auto_merge_enabled is set when validating merge trains

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/170652



Merged-by: Allison Browne <abrowne@gitlab.com>
Approved-by: Panos Kanellidis <pkanellidis@gitlab.com>
Approved-by: Allison Browne <abrowne@gitlab.com>
Reviewed-by: Allison Browne <abrowne@gitlab.com>
Co-authored-by: Hordur Freyr Yngvason <hfyngvason@gitlab.com>