CI: Drop permissions for container image build job

Author: markgoddard

.github/workflows/stackhpc-container-image-build.yml

@@ -68,6 +68,7 @@ jobs:
     name: Build Kolla container images
     if: github.repository == 'stackhpc/stackhpc-kayobe-config'
     runs-on: [self-hosted, stackhpc-kayobe-config-kolla-builder]
+    permissions: {}
     needs:
       - generate-tag
     steps:
@@ -205,6 +206,7 @@ jobs:
       - container-image-build
     if: github.repository == 'stackhpc/stackhpc-kayobe-config' && inputs.push
     runs-on: ubuntu-latest
+    permissions: {}
     steps:
       # NOTE(mgoddard): Trigger another CI workflow in the
       # stackhpc-release-train repository.