Rollup merge of #139880 - compiler-errors:rpitit-nameless, r=nnethercote

Don't compute name of associated item if it's an RPITIT

Use `Option::then` in favor of `Option::then_some` to not compute `AssocItem::name` if it fails the condition. Alternatively, I'd be open to changing this just to an `if`.

Fixes https://github.com/rust-lang/rust/issues/139873

r? ```@nnethercote```

compiler/rustc_hir_analysis/src/hir_ty_lowering/errors.rs

@@ -204,8 +204,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
             .iter()
             .flat_map(|trait_def_id| tcx.associated_items(*trait_def_id).in_definition_order())
             .filter_map(|item| {
-                (!item.is_impl_trait_in_trait() && item.as_tag() == assoc_tag)
-                    .then_some(item.name())
+                (!item.is_impl_trait_in_trait() && item.as_tag() == assoc_tag).then(|| item.name())
             })
             .collect();