Update to point at DS stable

The dependency-scanning job for this project was created pointing at a gemnasium-maven tagged docker image, because dependency-scanning was not yet updated with the latest version of gemnasium-maven which supports scala sbt projects.

Now that a new version of depency-scanning has been released https://gitlab.com/gitlab-org/security-products/dependency-scanning/pipelines/103830158 the tagged docker image can be removed from the ds ci job.