chore: added write permissions in the stale-discussions workflow (#26154)

Added write permission for github workflow action as required. This would eliminate the need for changing github repo settings as mentioned [here](https://github.com/aws-github-ops/handle-stale-discussions/blob/main/README.md#steps-to-enable-this-action-in-your-repository)
> [CONTRIBUTING GUIDE]: https://github.com/aws/aws-cdk/blob/main/CONTRIBUTING.md
> [DESIGN GUIDELINES]: https://github.com/aws/aws-cdk/blob/main/docs/DESIGN_GUIDELINES.md

Closes #<issue number here>.

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*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

Author: khushail

.github/workflows/handle-stale-discussions.yml

@@ -9,6 +9,8 @@ jobs:
   handle-stale-discussions:
     name: Handle stale discussions
     runs-on: ubuntu-latest
+    permissions:
+      discussions: write
     steps:
       - name: Stale discussions action
         uses: aws-github-ops/handle-stale-discussions@v1