add overlay vars

.gitlab-ci.yml

@@ -107,6 +107,13 @@ build:pages:
 check:links:
    stage: check
    image: docker
+   variables:
+     DOCKER_DRIVER: overlay2
+     # Create the certificates inside this directory for both the server
+     # and client. The certificates used by the client will be created in
+     # /certs/client so we only need to share this directory with the
+     # volume mount in `config.toml`.
+     DOCKER_TLS_CERTDIR: "/certs"
    services:
      - name: docker:dind
        command: ["--registry-mirror", "https://docker-registry.lcsb.uni.lu"]