Update 2FA troubleshooting docs

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/160727



Merged-by: Imre Farkas <ifarkas@gitlab.com>
Approved-by: Jon Glassman <jglassman@gitlab.com>
Approved-by: Marcel Amirault <mamirault@gitlab.com>
Approved-by: Imre Farkas <ifarkas@gitlab.com>
Reviewed-by: Marcel Amirault <mamirault@gitlab.com>
Co-authored-by: Brendan Lynch <blynch@gitlab.com>