Fix Windows support in coverage generation

[yannbf]

Closes #459

What I did

This PR attempts to fix a Windows compatibility issue when generating coverage. By using node to execute the binary file instead, it should work cross-platform.

Checklist for Contributors

Manual testing

This section is mandatory for all contributions. If you believe no manual test is necessary, please state so explicitly. Thanks!

Documentation

• [ ] Add or update documentation reflecting your changes in this repository
• [ ] Request documentation updates in the test-runner docs website

Checklist for Maintainers

• [ ] Make sure this PR contains one of the labels below:

  Available labels

  - `skip-release`: Skip any releases, e.g., documentation only changes, CI config etc. - `patch`: Upgrade patch version (e.g. 0.0.x) - `minor`: Upgrade patch version (e.g. 0.x.0) - `major`: Upgrade patch version (e.g. x.0.0)

📦 Published PR as canary version: 0.18.1--canary.461.2324514.0

:sparkles: Test out this PR locally via: ```bash npm install @storybook/test-runner@0.18.1--canary.461.2324514.0 # or yarn add @storybook/test-runner@0.18.1--canary.461.2324514.0 ```

[github-actions[bot]]

:rocket: PR was released in v0.18.2-next.0 :rocket: