ci: refine image-type for arm64

patch kata-containers#462(kata-containers/runtime#462)
has been restructured under upstream review, so refining image-type
to follow change.

Fixes: kata-containers#472

Signed-off-by: Penny Zheng <penny.zheng@arm.com>

.ci/lib_kata_image_aarch64.sh

@@ -6,7 +6,7 @@
 
 set -e
 
-IMAGE_TYPE="assets.image.meta.image-type-aarch64"
+IMAGE_TYPE="assets.image.architecture.aarch64.name"
 
 #packaged kata agent haven't been supported in any mainstream distribution
 get_packaged_agent_version() {