Improve error message when trying to call `issubclass()` against a Protocol that has non-method members

# Feature or enhancement

### Proposal:

The error message could tell the user what the non-method members in the protocol are.

### Has this already been discussed elsewhere?

This is a minor feature, which does not need previous discussion elsewhere

### Links to previous discussion of this feature:

_No response_


### Linked PRs
* gh-112344