feat: centralize cargo publish release condition

[bshek-xitaso]

In csaf and ssvc, the cargo publish job currently uses the same condition:

if: startsWith(github.ref, 'refs/tags/v') &&
    !contains(github.ref, 'beta') &&
    !contains(github.ref, 'alpha')

In vers-rs, publishing is instead controlled by the workflow trigger:

on:
  push:
    tags:
      - "v*"

Since we are planning to use the shared cargo publish workflow, perhaps the release condition could also be centralized there.

We should decide whether the publish policy should actually be the same for all repositories, especially regarding alpha and beta releases.

[peinjoh]

I'm in favor of centralizing (and aligning) that condition. Since we have not yet tagged anything with "beta" or "alpha" yet, I'm not sure how needed these two additional checks are, but lets discuss this further 👍