Missing images for contributors without GitHub accounts

For example on the [A Taste of Scala](https://docs.scala-lang.org/scala3/book/taste-intro.html) page:
![Screenshot 2024-11-20 at 15-37-37 A Taste of Scala Scala 3 — Book Scala Documentation](https://github.com/user-attachments/assets/1d0bfe4d-3c50-4535-9fca-78b208be72d9)