Logs in to Github Registry when preparing cache (#21069)

Whe we are preparing cache on CI, we should login to the
GitHub registry (using GITHUB_TOKEN) in order for --cache-to
to be able to push images.

scripts/ci/libraries/_build_images.sh

@@ -470,6 +470,8 @@ function build_images::build_ci_image() {
         exit 1
     fi
     if [[ ${PREPARE_BUILDX_CACHE} == "true" ]]; then
+        # we need to login to docker registry so that we can push cache there
+        build_images::login_to_docker_registry
         docker_ci_cache_directive+=(
             "--cache-to=type=registry,ref=${AIRFLOW_CI_IMAGE}:cache"
             "--load"
@@ -624,6 +626,8 @@ function build_images::build_prod_images() {
         exit 1
     fi
     if [[ ${PREPARE_BUILDX_CACHE} == "true" ]]; then
+        # we need to login to docker registry so that we can push cache there
+        build_images::login_to_docker_registry
         # Cache for prod image contains also build stage for buildx when mode=max specified!
         docker_cache_prod_directive+=(
             "--cache-to=type=registry,ref=${AIRFLOW_PROD_IMAGE}:cache,mode=max"