Bump unicode-bidi from 0.3.13 to 0.3.15 (#566)

Bumps [unicode-bidi](https://github.com/servo/unicode-bidi) from 0.3.13 to 0.3.15.
- [Release notes](https://github.com/servo/unicode-bidi/releases)
- [Commits](https://github.com/servo/unicode-bidi/commits)

---
updated-dependencies:
- dependency-name: unicode-bidi
  dependency-type: indirect
  update-type: version-update:semver-patch
...

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>