ci: have base install run in right dir

This sets the build dir at build time so that Apple SDK gets installed
in the correct/expected location for the runtime to find it.

Co-authored-by: Max Edwards <youwontforgetthis@gmail.com>

ci/test/02_run_container.sh

@@ -26,6 +26,7 @@ if [ -z "$DANGER_RUN_CI_ON_HOST" ]; then
       --file "${BASE_READ_ONLY_DIR}/ci/test_imagefile" \
       --build-arg "CI_IMAGE_NAME_TAG=${CI_IMAGE_NAME_TAG}" \
       --build-arg "FILE_ENV=${FILE_ENV}" \
+      --build-arg "BASE_ROOT_DIR=${BASE_ROOT_DIR}" \
       $MAYBE_CPUSET \
       --platform="${CI_IMAGE_PLATFORM}" \
       --label="${CI_IMAGE_LABEL}" \