Bump vitest and @vitest/coverage-istanbul

Bumps [vitest](https://github.com/vitest-dev/vitest/tree/HEAD/packages/vitest) and [@vitest/coverage-istanbul](https://github.com/vitest-dev/vitest/tree/HEAD/packages/coverage-istanbul). These dependencies needed to be updated together.

Updates `vitest` from 3.2.4 to 4.1.8
- [Release notes](https://github.com/vitest-dev/vitest/releases)
- [Changelog](https://github.com/vitest-dev/vitest/blob/main/docs/releases.md)
- [Commits](https://github.com/vitest-dev/vitest/commits/v4.1.8/packages/vitest)

Updates `@vitest/coverage-istanbul` from 3.2.4 to 4.1.8
- [Release notes](https://github.com/vitest-dev/vitest/releases)
- [Changelog](https://github.com/vitest-dev/vitest/blob/main/docs/releases.md)
- [Commits](https://github.com/vitest-dev/vitest/commits/v4.1.8/packages/coverage-istanbul)

---
updated-dependencies:
- dependency-name: vitest
  dependency-version: 4.1.8
  dependency-type: direct:development
- dependency-name: "@vitest/coverage-istanbul"
  dependency-version: 4.1.8
  dependency-type: direct:development
...

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Author: dependabot[bot]