(🐞) [1.15 REGRESSION] tuple fallback reports any expression

[KotlinIsland]

# mypy: allow-any-expr=False
a: tuple[int, int]
print(a[:]) # Expression type contains "Any" (has type "tuple[int, int]")  [misc]

playground

[sterliakov]

Exposed by #18585. At some point fallback is constructed as self.named_type("builtins.tuple") (there are several such places) and wrong Any (from_omitted_generics) ends up in slice tuple_fallback.

Minimal repro:

a: tuple[int, int]
print(a[:])