Automated Spec Update

 4a5fa1405ff0b7b5b388eedbbc02a72dd7956ff4

 Group all GitHub Actions updates into one PR

 7e5f66814d44d53f76b30049068bfb1ca27a0799

 This updates the spec dispatch workflow to use `peter-evans/repository-dispatch@v4` instead of the older v1 action. The workflow still dispatches the same `spec_update` event to the existing downstream repositories, but now explicitly disables default `GITHUB_TOKEN` permissions because remote dispatches are authenticated with `SPEC_UPDATE_TOKEN`.

This also sets `fail-fast: false` for the repository matrix so one failed downstream dispatch does not cancel the remaining dispatch attempts, and adds a small `client-payload` containing the source repository, ref, and commit SHA for downstream workflows that want to inspect where the spec update came from.

Author: dropbox-sdk-updater[bot]