Extend test to cover S.union with S.array

There might be an edge case when combining `S.union` with `S.array` so it would be great to extend the test cases to check for this.

e.g. a code snippet from my current project:

```ts
  export const Root = S.union({ RawInlineCategoryItem, RawItems: S.array(RawItem) })
  export type Root = RawInlineCategoryItem | RawItem[]
  ```