fix: cannot use must in bracket in fallback

[mzz2017]

Background

routing {
  # ...
  fallback: direct(must) # panic case
  fallback: must_direct # normal case
}

The above two cases should be equivalent, but one of them panics by mistake. This PR fixes this problem.

Checklist

• The Pull Request has been fully tested
• There's an entry in the CHANGELOGS
• There is a user-facing docs PR against https://github.com/daeuniverse/dae

Full Changelogs

• [Implement ...]

Issue Reference

Closes #[issue number]

Test Result

[dae-prow]

🧪 Since the PR has been fully tested, please consider merging it.