`ignore-missing` doesn't work with `compressed` & `download` configuration

[timnolte]

If I have a step that can't upload then there is no archive to download.

Upload: (step can soft-fail)

  - label: ":pipeline: Prime Cache"
    key: "prime-cache"
    soft_fail:
      - exit_status: 1
    command:
      - 'echo "--- Creating R Packages Cache..."'
    plugins:
      # Upload package cache to artifacts.
      # See https://github.com/buildkite-plugins/artifacts-buildkite-plugin
      - artifacts:
          ignore-missing: true
          upload: "${R_CACHE_LOCATION}"
          compressed: renv_cache.tgz

Download: (archive may not exist)

      - artifacts:
          step: "prime-cache"
          ignore-missing: true
          download: "${R_CACHE_LOCATION}/**/*"
          compressed: renv_cache.tgz

Originally posted by @timnolte in #89 (comment)