ci(contributors): drop force push from update workflow

The Update Contributors workflow runs on every push to main/dev plus a
weekly cron, and the auto-commit step was using push_options: '--force'.
Force push to a long-lived branch silently overwrites any commit that
landed between checkout and push (the concurrency group only guards the
workflow against itself, not against developer pushes).

The SVG is regenerable, so if a real conflict appears it's safe to let
the normal push reject and let the next scheduled run reconcile. Drop
the force flag.