[1.14 regression] False positive on abstract Enum subclasses in stubs

[JelleZijlstra]

While updating typeshed to mypy 1.14 (python/typeshed#13272), we got a few false positive errors on abstract enum classes like fpdf.enums.CoerciveEnum. This is due to the changes from #18068.

Perhaps we can throw the #18068 warning only if the enum class contains at least one attribute annotated with PEP 526 syntax. (cc @hauntsaninja as the author of #18068 and @tungol for the typeshed change.)