This... doesn't make much sense. An open-source license (one that is actually recognized as such by OSI[0]), means that anyone can fork the code and contribute to it at the very minimum. The only way to stop this would be to use a non open source license (or none at all, making it effectively source-available), but nobody would want to donate to someone making only source-available or closed-source projects.

The reality is that people would just have to choose, unfortunately.

[0]: https://opensource.org/licenses