[red-knot] micro-optimise ClassLiteral::is_protocol

[AlexWaygood]

Summary

I doubt it makes any significant difference to performance, but if Protocol is present in the bases list of a valid protocol class, it must either:

1. be the last base
2. or be the last-but-one base (with the final base being Generic[] or object)
3. or be the last-but-two base (with the penultimate base being Generic[] and the final base being object)

Test Plan

Existing tests pass

[github-actions]

mypy_primer results

No ecosystem changes detected ✅