Similar to how some other parts of the web UI support a `/latest` path
to directly go to the latest of a certain thing, let the Actions web UI
do the same: `/{owner}/{repo}/actions/runs/latest` will redirect to the
latest run, if there's one available.
Fixes gitea#27991.
Signed-off-by: Gergely Nagy <forgejo@gergo.csillger.hu>
