Allow uv-dev sync to update workflows (#20468)
The [initial `uv-dev` sync
run](https://github.com/astral-sh/uv/actions/runs/29501861094/job/87632531279)
was rejected with `refusing to allow a GitHub App to create or update
workflow without workflows permission` because the upstream update adds
`.github/workflows/sync-uv-dev.yml`. Request `workflows: write`
alongside `contents: write` so fork synchronization can propagate
workflow changes while keeping the token scoped to `uv-dev`.
Co-authored-by: Zanie Blue <contact@zanie.dev>
