Fix flatpak runtime upload

Embed runtime upload to images.apertis.org in build-runtime job instead of a separated job which consume runners and time.
Main runtime is uploaded to /srv/images/public/flatpak/mildenhall
MRs are uploaded to /srv/images/test/flatpak/mildenhall/$CI_COMMIT_REF_SLUG

Signed-off-by: Frédéric Danis frederic.danis@collabora.com