We'll still error due to the `opt_bad_ty` of `method_autoderef_steps`.
This slightly worsens the span of `infer_var.method()` which is now the
same as for `Box::new(infer_var).method()`.
Unlike `structurally_resolve_type`, `probe_op` does not check whether
the infcx is already tainted, so this results in 2 previously not emitted
errors.
