gha: stale: Bump stalebot version

- Bump the stalebot action version to v9 as that fixes the
```
Node.js 16 actions are deprecated. Please update the following actions to use Node.js 20: actions/stale@v8.
```
warning.

Fixes: #9512
Signed-off-by: stevenhorsman <steven@uk.ibm.com>

.github/workflows/stale.yaml

@@ -8,7 +8,7 @@ jobs:
   stale:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/stale@v8
+      - uses: actions/stale@v9
         with:
           stale-pr-message: 'This PR has been opened without with no activity for 180 days. Comment on the issue otherwise it will be closed in 7 days'
           days-before-pr-stale: 180