`accumulating` is annoying to use with the return ...

# arrow

[Youssef Shoaib [MOD]]

accumulating is annoying to use with the return value checker and Unit. If I want to e.g. verify some property, I won't be returning anything out of the accumulating, but the return value checker complains because I have ignored a RaiseAccumulate.Value<Unit>. Sadly, OverloadResolutionByLambdaReturnType doesn't seem like it'd help here.
Marking accumulating to be IgnorableReturnValue outright is not a good idea either. We don't want to allow expressions like:

accumulating { 3 }

to go by unchecked.