[ci] add more permissions for create-pull-request (#11302)

It seems like create pull request also needs content write permission

<img width="1008" height="465" alt="image"
src="https://github.com/user-attachments/assets/47d1b179-a887-4723-90ba-736f83ec2c4e"
/>


https://github.com/marketplace/actions/create-pull-request



current workflow error
```
  /usr/bin/git push --force-with-lease origin go_router-23310566202-1:refs/heads/go_router-23310566202-1
  remote: Permission to flutter/packages.git denied to github-actions[bot].
  fatal: unable to access 'https://github.com/flutter/packages/': The requested URL returned error: 403
  Error: The process '/usr/bin/git' failed with exit code 128
```

https://github.com/flutter/packages/actions/runs/23310566202/job/67796535425#step:3:884

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Author: chunhtai

.github/workflows/batch_release_pr.yml

@@ -45,7 +45,9 @@ jobs:
     if: needs.create_batch_release_branch.outputs.branch_created == 'true'
     runs-on: ubuntu-latest
     permissions:
-      pull-requests: write # Grants write permission to create a PR.
+      # The create-pull-request action needs both content and pull-requests permissions.
+      pull-requests: write
+      contents: write
     env:
       BRANCH_NAME: ${{ github.event.client_payload.package }}-${{ github.run_id }}-${{ github.run_attempt }}
     steps:

.github/workflows/sync_release_pr.yml

@@ -9,6 +9,10 @@ on:
 jobs:
   create_sync_pr:
     runs-on: ubuntu-latest
+    permissions:
+      # The create-pull-request action needs both content and pull-requests permissions.
+      contents: write
+      pull-requests: write
     steps:
       - name: Checkout repository
         uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd