stale.yml: do 5 operation per run

[Best practices for using the REST API](https://docs.github.com/en/rest/using-the-rest-api/best-practices-for-using-the-rest-api?apiVersion=2022-11-28)

.github/workflows/stale.yml

@@ -31,4 +31,4 @@ jobs:
           stale-pr-message: "This PR is stale because it has been open for 30 days with no activity."
           close-pr-message: "This PR was closed because it has been inactive for 14 days since being marked as stale."
           repo-token: ${{ secrets.GITHUB_TOKEN }}
-          operations-per-run: 100
+          operations-per-run: 5