stop vending alpha/beta releases as stable downstream artifacts

[qrkourier]

Problem: alpha/beta releases are vended as latest/stable in Linux package repos, at least

Context: Sometimes we need to publish an alpha/beta release in GitHub. That's cool, but the way we're building the Linux packages causes the alpha/beta to sort with a higher version in APT/DNF, so they're preferred over the stable release of the same major.minor.micro version, e.g., v1.2.6-beta2 is considered "latest" by APT even when v1.2.6 is released, but stable should always be higher.

Possible solutions:

1. filter out alpha/beta versions when promoting releases downstream from GitHub, such as Linux packages and Docker images.
2. change the way the downstream release artifacts are built and promoted so they're always sorted lower than a stable release of the same m.m.m

I'm leaning toward simply NOT promoting alpha/beta downstream.