collect_traces wrong return type when it's used as a decorator

[thepabloaguilar]

We're using the @context_manager decorator on collect_traces function, so, we can use it as a decorator or context manager.
When we use it as a decorator, the decorated function be with a wrong return type!!

Type safety test:

- case: collect_traces_context_manager_return_type
  disable_cache: true
  main: |
    from returns.primitives.tracing import collect_traces

    @collect_traces
    def function() -> int:
      return 0

    reveal_type(function)  # N: Revealed type is 'def () -> builtins.int'

Expected:

Revealed type is 'def () -> builtins.int'

Actual:

Revealed type is 'contextlib._GeneratorContextManager[None]'

Refs #441