Register rfcbot for Forge

[jieyouxu]

Since we do have a few FCPs going on there, and it'd be nice for the FCP labels to be used.

[github-actions]

Dry-run check results

[WARN  rust_team::sync] sync-team is running in dry mode, no changes will be applied.
[INFO  rust_team::sync] synchronizing crates-io
[INFO  rust_team::sync] synchronizing github
[INFO  rust_team::sync] 💻 Repo Diffs:
    📝 Editing repo 'rust-lang/rust-forge':
      Permission Changes:
        Giving user 'rust-rfcbot' write permission