The latest release that I see is 0.11.8.9 (see here) on GitHub, the container basically pulls the latest release from there, if they don't update it on GitHub I can't do anything about it...
The container is not like others, it updates itself on every start but you have to specify the Terraria version that it should pull in the template because the Terraria devs make my life really hard in terms of getting the version, so I changed over that the users have to enter the version that it should pull.