Comment by rty32

It is absolutely not common.

It is reasonable to expect contributors to have a certain amount of programming experience, but I rarely see any open source projects ask for requirements in a very specific area like a job posting. Many open source projects -- I am not talking about React or VSCode -- would be happy to see people creating pull requests at all, and are willing to provide pointers or hints for people who have experience but may not be so proficient in a specific language. Most of the projects work well that way.