stale-issues.yml: update to match main configuration

.github/workflows/stale-issues.yml

@@ -13,6 +13,7 @@ on:
  issue_comment:
 
 permissions:
+ contents: write
  issues: write
  pull-requests: write
 
@@ -45,6 +46,7 @@ jobs:
  recent activity. It will be closed if no further activity occurs.
  exempt-issue-labels: "gsoc-outreachy,help wanted,in progress"
  exempt-pr-labels: "gsoc-outreachy,help wanted,in progress"
+ delete-branch: true
 
  bump-pr-stale:
  if: >
@@ -68,3 +70,4 @@ jobs:
  pull request open, add a `help wanted` or `in progress` label.
  exempt-pr-labels: "help wanted,in progress"
  any-of-labels: "bump-formula-pr,bump-cask-pr"
+ delete-branch: true