Pin (and upgrade) immutable-eligible action actions/stale to their semantic versions

Author: mrecachinas

.github/workflows/stale.yaml

@@ -13,7 +13,7 @@ jobs:
       issues: write
       pull-requests: read
     steps:
-      - uses: actions/stale@28ca1036281a5e5922ead5184a1bbf96e5fc984e
+      - uses: actions/stale@9.0.0
         with:
           stale-issue-message: "This issue is stale because it has been open 21 days with no activity. Remove stale label or comment or this will be closed in 14 days."
           close-issue-message: "This issue was closed because it has been stalled for 35 days with no activity."