CI E2E: skip pushing the image to docker registry

Created by: eseliger

This also saves a second yarn execution.

It feels like this is a quick win and it shaves off around 20-30% runtime

Edit: Turns out we use the candidate image in the release process, so on the master branch we still need to push that image. But the above is still valid for non-master branches and it still saves around 1.5min on not running yarn twice and pulling the image again