ci: push "latest" to gitlab container registry with real tag name

Hello,

Made this quick PR to push to gitlab container registry with the real tag name (current one would be 1.3.0).

This will allow to select with more precision which version we want to use and have update jobs that would try to automatically update this version to the latest possible, without having to depend on latest, since it can break both our CI and usage workflow.

Not really familiar with GitLab's CI so feel free to edit this merge request.

Thank you !