With the potential move to branched based development in JDK mainline, and the change to default github action behavior proposed in JDK-8320358, we should change the naming model for branches in the backport fork repos. They are currently `<username>-backport-<hash>`. The username could potentially start with the string "jdk", which would clash with the new GHA filter rule. It would make more sense to name the branches `backport-<username>-<hash>, so that the backport branches have a clearly separated namespace.