chore: upgrade and fix the stale-issues workflow (#699)

This has been failing with the following error message for a while:

```
The workflow is not valid. .github/workflows/stale-issues.yml (Line: 20,
Col: 32): A sequence was not expected .github/workflows/stale-issues.yml
(Line: 21, Col: 29): A sequence was not expected
```

.github/workflows/stale-issues.yml

@@ -10,15 +10,15 @@ jobs:
       issues: write
       pull-requests: write
     steps:
-      - uses: actions/stale@v5
+      - uses: actions/stale@v7
         with:
           close-issue-message: 'Closing issue due to 30 days since being marked as stale.'
           days-before-issue-close: 30
           days-before-issue-stale: 90
           days-before-pr-close: -1
           days-before-pr-stale: -1
-          exempt-issue-labels: ['stale-exempt']
-          exempt-pr-labels: ['stale-exempt']
+          exempt-issue-labels: 'stale-exempt'
+          exempt-pr-labels: 'stale-exempt'
           repo-token: ${{ secrets.GITHUB_TOKEN }}
           stale-issue-label: 'stale'
           stale-issue-message: 'Marking as stale due to 90 days with no activity.'