[red-knot] Special case `@final`, `@override` (#17608)
## Summary
This PR adds special-casing for `@final` and `@override` decorator for a
similar reason as https://github.com/astral-sh/ruff/pull/17591 to
support the invalid overload check.
Both `final` and `override` are identity functions which can be removed
once `TypeVar` support is added.
