build(deps): bump xml-rs from 0.8.20 to 0.8.21 (servo#32943)

Bumps [xml-rs](https://github.com/kornelski/xml-rs) from 0.8.20 to 0.8.21.
- [Changelog](https://github.com/kornelski/xml-rs/blob/main/Changelog.md)
- [Commits](kornelski/xml-rs@0.8.20...0.8.21)

---
updated-dependencies:
- dependency-name: xml-rs
  dependency-type: indirect
  update-type: version-update:semver-patch
...

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Author: dependabot[bot]