Fix error message for calling a non-tuple struct

[Jamesbarford]

This feels a bit odd checking for "0" but I can't see how else to check for it being a Tuple

closes #148919

[rustbot]

r? @JonathanBrouwer

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[fmease]

I'm relatively sure the proper way to check if a definition is a tuple struct is something like:

let adt_def = tcx.adt_def(def_id);
adt_def.is_struct() && adt_def.non_enum_variant().ctor_kind() == Some(CtorKind::Fn)

No guarantees.