v1.22.2

This is a bugfix release for a type checker regression in v1.21.0.

Iterating an empty collection is rejected by the type checker

Policies that iterate a collection known to be empty, such as some x in [] or m[_] where m := {},
were rejected with rego_type_error: undefined ref. Iteration with a non-constant key is valid again, and simply
yields nothing. Comparing or unifying the elements of such a collection with a value is accepted as well.
Constant keys, like [][0], are still reported as undefined.

Reported by @kholia.