Require CI checks for beyond-refs PRs

[tmandry]

Requested in zulip.. #t-lang/custom-refs > Mapping out the solution space @ 💬

[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/beyond-refs':
      Branch Protections:
          main
            Requires PR: false => true
            Required Checks: [] => ["build"]
    📝 Editing repo 'rust-lang/bors':
      Rulesets:
          Ruleset for main
            No changes