Make release_download_test.sh work with ea builds

[sxa]

In order to ensure that we keep the download verification up to date with changes for each release we should ensure that the download script can work properly for early access builds.

At the moment it doesn't manage to select the artifacts correctly so the downloads aren't correct.

Once that's fixed, we need to ensure that the checks all work, although there is a known issue with the final check on the SHA which is mentioned in the script.

Related: Original issue at #3506