Try other ports when port 9000 is already used

### Pre-flight checklist

- [X] I have read the [contribution documentation](https://github.com/electron/forge/blob/main/CONTRIBUTING.md) for this project.
- [X] I agree to follow the [code of conduct](https://github.com/electron/electron/blob/main/CODE_OF_CONDUCT.md) that this project uses.
- [X] I have searched the issue tracker for a feature request that matches the one I want to file, without success.

### Problem description

When running `npm start` in a just-created project, I saw:

### Proposed solution

Try other ports when port 9000 is already used.

### Alternatives considered

- Not trying out other ports: status quo, 0 development required, but 0 support for other ports different than 9000.

### Additional information

Please.