Check if ModuleCancellationInstrumenter gracefully handles ref kind differences between original and replacement methods

I am wondering if any unexpected behavior changes could occur if:
- the original method was a `readonly` struct method and the replacement method was not, for example.
- Or, the other way around, the original is non-readonly and the replacement is readonly.

Since it seems like we are not checking the readonly-ness of the `this` parameter in these checks.

Since this PR is already merged some time ago, I will open a new issue based on this comment.

_Originally posted by @RikkiGibson in https://github.com/dotnet/roslyn/pull/71896#discussion_r1678293932_