Change close command to 'close not-planned' for rotten

Closing as completed is misleading on inactive issues.

Utilizes kubernetes-sigs/prow@b03af6d

Author: kaovilai

ci-operator/jobs/infra-periodics.yaml

@@ -377,7 +377,7 @@ periodics:
         Mark the issue as fresh by commenting `/remove-lifecycle rotten`.
         Exclude this issue from closing again by commenting `/lifecycle frozen`.
 
-        /close
+        /close not-planned
       - --template
       - --ceiling=10
       - --confirm