update permissions in caller workflow (#318)

Signed-off-by: rulex123 <erica.manno@gmail.com>

Author: rulex123

.github/workflows/scheduled.yml

@@ -14,7 +14,7 @@ jobs:
 
   call-update-protobuf:
     permissions:
-      contents: read
+      contents: write
       pull-requests: write
     needs: call-compare-envoy-versions-workflow
     if: ${{ needs.call-compare-envoy-versions-workflow.outputs.target-version != 'noop' }}