99% of the time, your “use” of starter content means that your project REFERENCES the content, and the content actually lives in the Unreal Engine folder, which you do not copy or check into a public github repository.
This is no different from a .h file of yours #including <Engine.h> from Unreal – the copyright does not convey through that reference.
(Separately, the “viral” licenses use your use of their code under copyright as a lever to apply other licensing terms that are not directly related to copyright – using #include for GPL code is not recommended unless everything is GPL!)