Use zuul_legacy_vars for propose jobs for now
We need to rework this completely to be v3 native. For now, just grab
the legacy vars.
command: "{{ ansible_user_dir }}/scripts/propose_update.sh {{ update_target }}"
args:
chdir: "src/{{ zuul.project.canonical_name }}"
+ environment: '{{ zuul | zuul_legacy_vars }}'
