Retry resolution and connection failures in release downloads (#12641)

Release run 34851108495 (v0.64.23) failed twice on a runner DNS blip after
the 40-minute build: once in the cmux-tui client resolver and once in
ensure-sentry-cli.sh ("curl: (6) Could not resolve host: github.com"),
which skipped every publish step. curl's --retry only covers transient
HTTP codes, so the sentry-cli download and the cmux-tui manifest and
slice downloads now also pass --retry-all-errors and --retry-connrefused
with a bounded delay, so a blip retries instead of failing the release.

Co-authored-by: Claude Fable 5.1 <noreply@anthropic.com>