Current situation

The regular update test was using the nightly payload from bincache and after seeing this issue it is now skipped:
https://github.com/flatcar/scripts/blob/6bec600278c863c7bf5e2755db10e491b7225f18/ci-automation/vendor-testing/qemu_update.sh#L30

Impact

While possible to test for each PR it is not done

Ideal future situation

The GitHub Action copies the artifact from the build step over to the right location (either directly to the location expected by if [ -f "${QEMU_UPDATE_PAYLOAD}" ] ; then or change the logic there to find it and copy it over). Also remove the TODO comment.
https://github.com/flatcar/scripts/blob/6bec600278c863c7bf5e2755db10e491b7225f18/ci-automation/vendor-testing/qemu_update.sh#L30