mesh-2092: move write permissions to job level

Author: james-bradley-nhs

.github/workflows/dependabot-auto-merge.yaml

@@ -14,9 +14,6 @@ jobs:
     # Only run on Dependabot PRs
     if: github.event.pull_request.user.login == 'dependabot[bot]'
     runs-on: ubuntu-latest
-    permissions:
-      contents: write
-      pull-requests: write
 
     steps:
       - name: Checkout