[3.12] gh-120361: Add `nonmember` test with enum flags inside to `test_enum` (GH-120364) (#120512)

gh-120361: Add `nonmember` test with enum flags inside to `test_enum` (GH-120364)

* gh-120361: Add `nonmember` test with enum flags inside to `test_enum`
(cherry picked from commit 7fadfd82ebf6ea90b38cb3f2a046a51f8601a205)

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