ci: remove box download timeout in upstream tests

[nbusseneau]

This timeout can be too small when the host has to download all boxes due to not having any of the boxes required for the SHA to be tested.

In particular this is prone to happen on backport PRs, since it's more likely for the job to be scheduled on a node that primarily run master pipelines up to that point.

[christarazi]

I assume there's no risk that the download hangs in some way?

[nbusseneau]

The other Jenkinsfiles do not have a timeout and we never hit an issue with that. In the worst case it'll hit the global job timeout, but I don't think this ever happened because of the download times, so I think we should be good 😄

[nbusseneau]

It appears we've made a mistake in #18741 and this PR was actually not backported to v1.9. I am resetting backport status.

@joestringer This PR was mentioned in the release notes for v1.9.13, but was actually not backported properly and will be instead added to the next round of backports. Just mentioning it in passing, but it's not actually very important since it has no user-facing consequences.

[joestringer]

CC @joamaki in case you do backports in future, please make sure to update the PR description (both the text and the command for updating the labels) if you remove any PRs. We use that as the source of truth for marking PRs as backported, and for generating release notes.

[nbusseneau]

Just in case: I don't think this was intended and the PR was removed intentionally. I had acked the backport changes myself on the PR, so either I got confused and acked the wrong PR or we mistakenly removed the PR afterwards in a later push.