ci: use buildx in ci

Github-Pull: #32989
Rebased-From: 94a0932547

This rebase also includes part of e87429a2d0
adding `$DOCKER_BUILD_CACHE_ARG \` to the `docker build` command.

Using buildx is required to properly load the correct driver, for use
with registry caching. Neither build, nor BUILDKIT=1 currently do this
properly.

Use of `docker buildx build` is compatible with podman.

ci/test/02_run_container.sh

@@ -17,11 +17,15 @@ if [ -z "$DANGER_RUN_CI_ON_HOST" ]; then
   docker run --rm "${CI_IMAGE_NAME_TAG}" bash -c "env | grep --extended-regexp '^(HOME|PATH|USER)='" | tee --append "/tmp/env-$USER-$CONTAINER_NAME"
   echo "Creating $CI_IMAGE_NAME_TAG container to run in"
 
-  DOCKER_BUILDKIT=1 docker build \
+  # Use buildx unconditionally
+  # Using buildx is required to properly load the correct driver, for use with registry caching. Neither build, nor BUILDKIT=1 currently do this properly
+  # shellcheck disable=SC2086
+  docker buildx build \
       --file "${BASE_READ_ONLY_DIR}/ci/test_imagefile" \
       --build-arg "CI_IMAGE_NAME_TAG=${CI_IMAGE_NAME_TAG}" \
       --build-arg "FILE_ENV=${FILE_ENV}" \
       --label="${CI_IMAGE_LABEL}" \
+      $DOCKER_BUILD_CACHE_ARG \
       --tag="${CONTAINER_NAME}" \
       "${BASE_READ_ONLY_DIR}"