[3.11] gh-103592: Add tests of `Literal` with `Enum` and `Union` of `Literal`s (GH-103706) (#103720)

gh-103592: Add tests of `Literal` with `Enum` and `Union` of `Literal`s (GH-103706)
(cherry picked from commit 5041c2ba6e9c992d1c54834481c9be64581c0235)

Co-authored-by: Nikita Sobolev <mail@sobolevn.me>