chore(deps-dev): bump @web/test-runner from 0.18.3 to 0.20.2

Bumps [@web/test-runner](https://github.com/modernweb-dev/web/tree/HEAD/packages/test-runner) from 0.18.3 to 0.20.2.
- [Release notes](https://github.com/modernweb-dev/web/releases)
- [Changelog](https://github.com/modernweb-dev/web/blob/master/packages/test-runner/CHANGELOG.md)
- [Commits](https://github.com/modernweb-dev/web/commits/@web/test-runner@0.20.2/packages/test-runner)

---
updated-dependencies:
- dependency-name: "@web/test-runner"
  dependency-version: 0.20.2
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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Author: dependabot[bot]