ansible: docker: update apt key install method
Fix that the deprecated method for installing the apt key for the docker
repository was still used.
Fix for (with debian 13):
Failed to find required executable "apt-key" in paths: /usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
Related: OS#6998
Change-Id: I8184b6f9369886b79a3cf015ceee6e46e38b089c
