Do not retry on not found resource

[leakingtapan]

We found Buildkite agent retry on 404 when downloading artifacts, but this is unnecessary. Since we have extended retry (up to 30 mins), the current behavior (retry on 404) largely slows down the progress to fail fast. So add the small patch to skip retry on 404 for artifact download.

[leakingtapan]

@lox

[lox]

I'm no longer Buildkite staff @leakingtapan! Just a contributor like yourself.

[leakingtapan]

@lox ah, got it.

[leakingtapan]

@moskyb could you take a look? thx