Fix ptr slices assertions in js nk module arguments (#1150)

Goja introduced the following change:
https://github.com/dop251/goja/commit/7749907a8a20719efef6c6fb4d39f2ba64f7557c
JS arrays backed by a Go slice referenced by a pointer would be
returned by .Export() as []S, but now are returned as *[]S which requires
changing all the type assertions when dealing with these values.