Bump tar-fs and @web/test-runner

Bumps [tar-fs](https://github.com/mafintosh/tar-fs) to 3.0.8 and updates ancestor dependency [@web/test-runner](https://github.com/modernweb-dev/web/tree/HEAD/packages/test-runner). These dependencies need to be updated together.


Updates `tar-fs` from 2.1.1 to 3.0.8
- [Commits](mafintosh/tar-fs@v2.1.1...v3.0.8)

Updates `@web/test-runner` from 0.15.0 to 0.20.0
- [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/[email protected]/packages/test-runner)

---
updated-dependencies:
- dependency-name: tar-fs
  dependency-version: 3.0.8
  dependency-type: indirect
- dependency-name: "@web/test-runner"
  dependency-version: 0.20.0
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]