ci: Use non-deprecated sentry-cli snapshots upload command (#5774)

The `sentry-cli build snapshots` command is deprecated in favor of
`sentry-cli snapshots upload`. Rename both usages in CI so the upload
steps stop emitting deprecation warnings and keep working once the old
command is removed.

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>