artifact download URL is not resumable

From this buildomat run:
https://github.com/oxidecomputer/omicron/runs/38078608713

I wanted to download /work/repo.zip, which is:
https://buildomat.eng.oxide.computer/wg/0/artefact/01JND89XBVFYKYFJXD6JFDA8XR/i361qB3lfswvUlvUnk2I8TAIInnC6R0aVLrufUE3xiKZ7Jpm/01JND8A832Z6DMSNDE05HMFHVH/01JNDBQH91APJC86M538P066PN/repo.zip

That seems to reliably fail to download just after the 1 GiB mark (a separate bug):

$ curl -O https://buildomat.eng.oxide.computer/wg/0/artefact/01JND89XBVFYKYFJXD6JFDA8XR/i361qB3lfswvUlvUnk2I8TAIInnC6R0aVLrufUE3xiKZ7Jpm/01JND8A832Z6DMSNDE05HMFHVH/01JNDBQH91APJC86M538P066PN/repo.zip
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
 50 2039M   50 1030M    0     0  5613k      0  0:06:12  0:03:07  0:03:05 5476k
curl: (92) HTTP/2 stream 1 was not closed cleanly: INTERNAL_ERROR (err 2)

I tried to retry it but:

$ curl -C- -O https://buildomat.eng.oxide.computer/wg/0/artefact/01JND89XBVFYKYFJXD6JFDA8XR/i361qB3lfswvUlvUnk2I8TAIInnC6R0aVLrufUE3xiKZ7Jpm/01JND8A832Z6DMSNDE05HMFHVH/01JNDBQH91APJC86M538P066PN/repo.zip
** Resuming transfer from byte position 1080246028
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
  0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0
curl: (33) HTTP server does not seem to support byte ranges. Cannot resume.

This looks similar to #31, but the fix for that looks like it was fixing a different endpoint (/public/file/...).

Reproduce the failure with the artifact URL and curl -C-, then compare this endpoint with the /public/file/... endpoint discussed in #31. Identify how the artifact download responds to byte-range requests and verify that an interrupted transfer can resume successfully without changing the requested URL.