Update stale.yaml

Adding pinned version to get past this error https://github.com/github/advisory-database/actions/runs/9200192452

.github/workflows/stale.yaml

@@ -10,7 +10,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-    - uses: actions/stale@latest
+    - uses: actions/stale@v9.0.0
       name: Clean up stale PRs
       with:
         repo-token: ${{ secrets.STALE_BOT }}