Bump @vitest/coverage-v8 from 2.1.9 to 4.0.6 in /cirq-web/cirq_web

Bumps [@vitest/coverage-v8](https://github.com/vitest-dev/vitest/tree/HEAD/packages/coverage-v8) from 2.1.9 to 4.0.6.
- [Release notes](https://github.com/vitest-dev/vitest/releases)
- [Commits](https://github.com/vitest-dev/vitest/commits/v4.0.6/packages/coverage-v8)

---
updated-dependencies:
- dependency-name: "@vitest/coverage-v8"
  dependency-version: 4.0.6
  dependency-type: direct:development
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]