build: use VK S3 for icu4c and zziplib archives

The CI/CD builds are performed on VK Cloud virtual machines, so the
access to VK S3 is more reliable than to GitHub archives.

In fact, we experience periodical download problems with source archives
on GitHub in Tarantool Enterprise Edition builds in CI/CD and it is the
motivation to backup the archives on our side. The problems appear quite
frequently last few days.

The download problems are not on VK Cloud side and not on GitHub side.
The packet loss is somewhere in the middle. I don't know an exact reason
for now.

NO_DOC=no user-visible changes
NO_CHANGELOG=see NO_DOC
NO_TEST=see NO_DOC