Don't mark as stale issues and PRs with a milestone

Author: bbatsov

.github/workflows/stale.yml

@@ -15,6 +15,7 @@ jobs:
           days-before-issue-stale: 30
           days-before-issue-close: 30
           stale-issue-label: "stale"
+          exempt-all-milestones: true
           exempt-issue-labels: "bug, high priority, good first issue, pinned"
           stale-issue-message: >-
             This issue has been automatically marked as stale because it has not