Error sync if a private repo is not marked as private in team

[Kobzol]

If a repository is private, we have to properly mark it as such in the team database, because some bots can depend on this.

Note that we cannot check this only in validation, because we could not distinguish private and missing repositories without a privileged auth token (a non-privileged one, such as the one in PR CI, would just see that the repo does not exist).

[github-actions]

Dry-run check results

[WARN  sync_team] sync-team is running in dry mode, no changes will be applied.
[INFO  sync_team] synchronizing crates-io
[INFO  sync_team] synchronizing github
[INFO  sync_team] 💻 Repo Diffs:
    📝 Editing repo 'rust-lang/bors':
      Rulesets:
          Ruleset for main
            No changes