Thanks (also to Jacob Keller), the git-notes might work in some cases.
But it's obviously a pasted-on solution, requiring a different usage,
e.g. "git log --notes", and whatever other UIs do with it.
One more thing, if you know that no one has fetched the branch you just
pushed yet, you can amend the commit and force-push it without any
problems (I'd sugget using --force-with-lease).
In my particular case, not going to work, multiple CI engines jump
hungry at every commit.