For a regular block, accepting two arguments is fine as the array
will be autosplatted.   However, a lambda that accepts two arguments
will not work.

We could change the implementation to yield two arguments instead
of an array with a single argument, but that would be less backwards
compatible.

I'm only changing the call-seq to be precise, other examples pass
a literal block that accepts two arguments, and I left those alone
as that will be the most common usage.

Fixes [Bug #17094]