Cache save failure is silently successful

I have a job with a cache save action step like:

  - name: Cache build directory
    uses: actions/cache@v2
    with:
      path: ./build
      key: ${{ env.CACHE_VERSION }}-build-test
      restore-keys: |
        ${{ env.CACHE_VERSION }}-build-test

This step fails with a warning from the cache service with 500 error:

Post job cleanup.
/usr/bin/docker exec 753ebc673e8c0bc1348b4c7c70cc7e429e7a567cc043866fb5d2a3684a233e5c sh -c "cat /etc/*release | grep ^ID"
/usr/bin/tar --posix -z -cf cache.tgz -P -C /__w/work-dir --files-from manifest.txt
Warning: uploadChunk (start: 0, end: 33554431) failed: Cache service responded with 500

That warning handling leads to successful job completion, and other job failing that tries to restore this cache later.

I believe the save cache action should fail on an error returned by the caching service.

Start by tracing the cache save path that handles the uploadChunk warning shown during post-job cleanup. Verify how cache-service errors are converted into the action result; done means a failed save causes the job to fail instead of completing successfully. The payload does not name a source file or test.