Tell git to not care about repo ownership for downstream builds

function prepare_downstream_build()

{

  # Repo ownership is adventurous in gitlab runner, we don't care.

  git config --global --add 'safe.directory' '*'

  # NOTE: parses https://github.com/user/repo.git@branch_name

  local proj_url="${1%%@*}"

  local proj_branch=${1#"${proj_url}@"}