ci: add close issue reason to stale workflow

Author: EndBug

.github/workflows/stale.yml

@@ -22,5 +22,6 @@ jobs:
             for your contributions.
           stale-issue-label: 'status: stale'
           stale-pr-label: 'status: stale'
+          close-issue-reason: not_planned
           exempt-issue-labels: 'pinned,security,status: pinned,type: security'
           exempt-pr-labels: 'pinned,security,status: pinned,type: security'