use buildx build driver

Author: willcl-ark

ci/test/02_run_container.sh

@@ -47,7 +47,7 @@ if [ -z "$DANGER_RUN_CI_ON_HOST" ]; then
   fi
 
   # shellcheck disable=SC2086
-  DOCKER_BUILDKIT=1 docker build \
+  DOCKER_BUILDKIT=1 docker buildx \
       --file "${BASE_READ_ONLY_DIR}/ci/test_imagefile" \
       --build-arg "CI_IMAGE_NAME_TAG=${CI_IMAGE_NAME_TAG}" \
       --build-arg "FILE_ENV=${FILE_ENV}" \