Lint `conflicting_repr_hint` should explain how to update flagged code

[gonzalobg]

My app using #[repr(C, u8)] enum to FFI with a C++ enum class : uint8_t {} stopped compiling when updating the toolchain.

The warning produced does not explain how to update this code.
The warning points to: #68585
In which this comment says that my code is the obvious way to do that: #68585 (comment)

The warning should explain how to update my code so that it continues working correctly.