Fix GHA backport.yaml workflow job perms

Fixing backport workflow permissions.

Signed-off-by: Aurel Canciu <aurelcanciu@gmail.com>

.github/workflows/backport.yaml

@@ -10,6 +10,9 @@ permissions:
 jobs:
   pull-request:
     runs-on: ubuntu-latest
+    permissions:
+      contents: write
+      pull-requests: write
     if: github.event.pull_request.state == 'closed' && github.event.pull_request.merged && (github.event_name != 'labeled' || startsWith('backport:', github.event.label.name))
     steps:
       - name: Checkout