update the released package name in Docker image construction

[Geal]

We changed the released package names in #1393 to include the full
target triplet

⚠️ do not merge this until we have published a release containing #1393

[github-actions]

@Geal your pull request is missing a changelog!

[garypen]

Good timing. I was just going to do that!

[garypen]

Hmm, now that I've approved it, it does mean that it will only work from the next release forwards. We'll have to watch out for that if anyone files an issue.

[abernix]

@Geal @garypen Couldn't both the waiting for the release and the "forward support only" both be avoided if we used the installer script rather than the direct link to the tarball? The installer script works off GitHub Releases so the latest points to the latest release and the installer that gets used is based on the install.sh script rather than the hard-coded link to the tarball.

I'd also argue that we should be doing that anyways to make sure all the downloads are going through an endpoint that we control. If that makes sense, I'm happy to make a PR.

[garypen]

I think the existing code pre-dates the creation of the installer script, so bringing it into line with the installer seems sensible.
Would there be a timing issue during the processing of the release?

I presume the PR would be to replace the explicit ADD of a version with a RUN of the installer?

[Geal]

closing in favor of #1629