Fix PNC + ? suffix interaction

[smores56]

module [something]

something = |_|
    ["hello"] |> List.first()?

> cargo run --bin roc -- check test2.roc
...

── TYPE MISMATCH in ../test2.roc ───────────────────────────────────────────────

This returns something that's incompatible with the return type of the
enclosing function:

4│      ["hello"] |> List.first()?
        ^^^^^^^^^^^^^^^^^^^^^^^^^

This returns an Err of type:

    [Err [ListWasEmpty]]

But I expected the function to have return type:

    Str

────────────────────────────────────────────────────────────────────────────────

1 error and 0 warnings found in 121 ms.