ci: Use actions/download-artifact@v3

This commit updates the CI workflows to use the download-artifact
action v3, which is based on node.js 16 and @actions/core 1.10.0, in
preparation for the upcoming removal of the deprecated GitHub features.

Signed-off-by: Stephanos Ioannidis <root@stephanos.io>
(cherry picked from commit 494bb013)