I was also stuck at 12.9.2 as standard apt-get upgrade wouldn’t pull any newer versions like it used to. After this I did:
apt-get install gitlab-ce=12.9.3-ce.0
and have done this for all 12.9.x releases, as well as 12.10.x releases to get to 12.10.14 yesterday. This worked for me without any issues, although I expect I could have jumped a few of the releases.
Did you try upgrading like the above command and it failed? If so, were there any error messages?