We have a Git repo where have a Dockerfile that’s built and pushed to a registry. We want to simply run this Docker image in a Task. But when we try to do this, the Agent seems to also clone the entire repository every time the Task is run. This is not desired as we copy the repository code already inside the Dockerfile. Anyway to disable this repeated cloning?

Do you mean there's a prebuilt docker image available in some docker registry? The agent does not build a docker image from a Dockerfile.