ci: add read-only pull secret to security build

.woodpecker/build-container.yml

@@ -12,6 +12,8 @@ steps:
       containerfile: Containerfile.multiarch
       output: type=oci,dest=oci/${CI_REPO_NAME},tar=false
       repo: ${CI_REPO}
+      registry_config:
+        from_secret: DOCKER_REGISTRY_CONFIG_PULL
 
   - name: security-scan
     image: docker.io/aquasec/trivy