Update actions/stale action to v6 (#157)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

.github/workflows/stale.yml

@@ -10,7 +10,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-    - uses: actions/stale@v5
+    - uses: actions/stale@v6
       with:
         repo-token: ${{ secrets.GITHUB_TOKEN }}
         stale-issue-message: 'This issue has been marked as stale due to inactivity. If this issue is still ongoing, please leave a comment.'