gh-74690: Don't set special protocol attributes on non-protocol subclasses of protocols by AlexWaygood · Pull Request #104622 · python/cpython
This was a small oversight in #103160. It's not a huge issue by any means, but there's no reason to set the special __protocol_attrs__ and __callable_proto_members_only__ attributes for concrete subclasses of protocols, and if we skip doing so, we speedup class creation by around 33%.
(Skipping news, since this fixes a small oversight in a commit that hasn't been included in any released version of Python.)