CI: Drop permissions for package promote job

Author: markgoddard

.github/workflows/stackhpc-promote.yml

@@ -11,6 +11,7 @@ jobs:
     name: Trigger package repository promotion
     if: github.repository == 'stackhpc/stackhpc-kayobe-config'
     runs-on: ubuntu-latest
+    permissions: {}
     steps:
       # NOTE(mgoddard): Trigger another CI workflow in the
       # stackhpc-release-train repository.