The utility function `clippy_utils::fulfill_or_allowed` is not used because
using it would require to move the check for allowed after the check
iterating over all inherent impls of the type, doing possibly
unnecessary work.
Instead, `is_lint_allowed` is called as before, but additionally, once
certain that the lint should be emitted, `span_lint_hir_and_then` is called
instead of `span_lint_and_help` to also fulfill expectations.
fixes: #12802
changelog: fulfill expectations in `check_unsafe_derive_deserialize`
fc2f7035c6