build(deps-dev): bump @microsoft/api-extractor from 7.20.0 to 7.21.3 (#1643)

Bumps [@microsoft/api-extractor](https://github.com/microsoft/rushstack/tree/HEAD/apps/api-extractor) from 7.20.0 to 7.21.3.
- [Release notes](https://github.com/microsoft/rushstack/releases)
- [Changelog](https://github.com/microsoft/rushstack/blob/main/apps/api-extractor/CHANGELOG.md)
- [Commits](https://github.com/microsoft/rushstack/commits/@microsoft/api-extractor_v7.21.3/apps/api-extractor)

---
updated-dependencies:
- dependency-name: "@microsoft/api-extractor"
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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