v49: Release swh.lister v5.7.1

Test to ascertain the scripted part in build-docker-images [1] works as expected (it does ;).

git push -o merge_request.create -o merge_request.target=staging -o 'merge_request.title=v49: Release swh.lister v5.7.1' -o merge_request.remove_source_branch=true origin swh-next-version

[1] https://jenkins.softwareheritage.org/job/swh-apps/job/build-docker-images/9/console