Add last major to dropdown
What does this MR do and why?
When a new major GitLab version is released, we tend to not include the last major in the last_majors list in versions.json, because that would cause duplicate entries in the main site's dropdown. Here how it was done in the 16.0 release !3864 (comment 1400673875).
However, doing so, caused not one, but two bugs to happen!
This change adds the last major in the dropdown to fix two issues:
This will duplicate the entries, but it will make the bugs go away for the time being until a permanent fix is in place.
Edited by Achilleas Pipinellis