chore: Update stale issues GitHub action to use last stable v6 version.

Author: ashishdhingra

.github/workflows/stale_issues.yml

@@ -10,7 +10,7 @@ jobs:
     runs-on: ubuntu-latest
     name: Stale issue job
     steps:
-    - uses: aws-actions/stale-issue-cleanup@main
+    - uses: aws-actions/stale-issue-cleanup@v6
       with:
         # Setting messages to an empty string will cause the automation to skip
         # that category