No compile error when returning incorrect aliased struct

[Tetralux]

This should have been a compile error:

https://github.com/Tetralux/zig/blob/24aea24c22627c415d81339749e8a94a7239af1a/std/http/headers.zig#L173

.iteratorConst returns a completely different struct to HttpList.Iterator...

Originally posted by @Tetralux in #3037 (comment)

[Tetralux]

Note that iteratorConst is defined here:

https://github.com/Tetralux/zig/blob/24aea24c22627c415d81339749e8a94a7239af1a/std/array_list.zig#L278

[andrewrk]

can you come up with a reduction?