Ignore bugs in issue staleness checks

Author: bbatsov

.github/workflows/stale.yml

@@ -15,7 +15,7 @@ jobs:
           days-before-issue-stale: 30
           days-before-issue-close: 30
           stale-issue-label: "stale"
-          exempt-issue-labels: "high priority, good first issue, pinned"
+          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
             had any recent activity. It will be closed soon if no further