ci: use a newer `github-script` version

ci: use a newer `github-script` version

The old version we currently use runs in node.js v12.x, which is being
deprecated in GitHub Actions. The new version uses node.js v16.x.

Incidentally, this also avoids the warning about the deprecated
`::set-output::` workflow command because the newer version of the
`github-script` Action uses the recommended new way to specify outputs.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Taylor Blau <me@ttaylorr.com>