ci/github-script/bot: don't attempt to fetch pagination cursor if it's expired

I fixed this for the maintainer maps, but the artifact that was causing the
particular issue that prompted me to try to fix it was actually the
pagination cursor. So fix that too.

Related: #464046.

ci/github-script/bot.js

@@ -609,7 +609,7 @@ module.exports = async ({ github, context, core, dry }) => {
         ).data.artifacts[0]
 
         // If the artifact is not available, the next iteration starts at the beginning.
-        if (artifact) {
+        if (artifact && !artifact.expired) {
           stats.artifacts++
 
           const { downloadPath } = await artifactClient.downloadArtifact(