Fix a race that let the Action fail quite often

Switch to node.js 20

Let's use Node v16.x!

This version allows to specify a reasonFilter

With this change, this Action can restrict further from which build to
download the artifact.

This version avoids short downloads

On rare occasion, we encountered situations where the artifact files
were downloaded only incompletely, yet the Action reported success (and
cached the incomplete set of files). We now ensure that the total bytes
written to disk match the expected value before allowing the Action to
succeed.

The first public version of this GitHub Action