Update stale.yml [skip ci]

Author: stefmolin

.github/workflows/stale.yml

@@ -13,7 +13,7 @@ jobs:
   stale:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/stale@v4
+      - uses: actions/stale@28ca1036281a5e5922ead5184a1bbf96e5fc984e  # v9.0.0
         with:
           days-before-stale: 30
           days-before-close: 7