The warning was written for the bulk upload only, and counted lines:
latest.json is uploaded by a second rclone call, which could still pass
on a retry unseen, and a file that failed on two attempts was counted as
two uploads.
Both calls go through test/vm-image/nightly-rclone, which passes
rclone's output and exit status through and names each file once. A
stand-in rclone tests it.
