Change type signatures of `Data.List.NonEmpty.intersect` and `Data.List.NonEmpty.intersectBy` to return a `List` instead of a `NonEmptyList`

[evaogbe]

Description of the change

Clearly and concisely describe the purpose of the pull request. If this PR relates to an existing issue or change proposal, please link to it. Include any other background context that would help reviewers understand the motivation for this PR.

Changed type signatures of Data.List.NonEmpty.intersect and Data.List.NonEmpty.intersectBy to return a List instead of a NonEmptyList. Fixes #216

---

Checklist:

• [x] Added the change to the changelog's "Unreleased" section with a reference to this PR (e.g. "- Made a change (#0000)")
• [x] Linked any existing issues or proposals that this pull request should close
• [x] Updated or added relevant documentation
• [x] Added a test for the contribution (if applicable)