Bump @webref/events from 1.20.2 to 1.21.0

Bumps [@webref/events](https://github.com/w3c/webref) from 1.20.2 to 1.21.0.
- [Commits](https://github.com/w3c/webref/compare/@webref/events@1.20.2...@webref/events@1.21.0)

---
updated-dependencies:
- dependency-name: "@webref/events"
  dependency-version: 1.21.0
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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Author: dependabot[bot]