Add back branch protection for expect-test

[Kobzol]

The expect-test repo had quite weird branch protections (#1805): both pr-required = false and non-empty ci-checks. In #1805, I removed the CI check, but I think it actually makes more sense to require PRs and the CI check, unless someone asks for the opposite.

[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 github
[INFO  sync_team] 💻 Repo Diffs:
    📝 Editing repo 'rust-analyzer/expect-test':
      Branch Protections:
          master
            Required Approving Review Count: 0 => 1
            Requires PR: false => true
            Required Checks: [] => ["test"]