Fix test image upload (#4229)

Author: dsimansk

test/upload-test-images.sh

@@ -30,9 +30,17 @@ function upload_test_images() {
     tag_option="--tags $docker_tag,latest"
   fi
 
+  # If PLATFORM environment variable is specified, then images will be built for
+  # specific hardware architecture.
+  # Example of the variable values - "linux/arm64", "linux/s390x".
+  local platform=""
+  if [ -n "${PLATFORM}" ]; then
+    platform="--platform ${PLATFORM}"
+  fi
+
   # ko resolve is being used for the side-effect of publishing images,
   # so the resulting yaml produced is ignored.
-  ko resolve ${KO_FLAGS} ${tag_option} -RBf "${image_dir}" >/dev/null
+  ko resolve ${platform} ${tag_option} -RBf "${image_dir}" >/dev/null
 }
 
 : ${KO_DOCKER_REPO:?"You must set 'KO_DOCKER_REPO', see DEVELOPMENT.md"}