use DefineOpaqueTypes::Yes in rustdoc

Since we have a `DefiningAnchor::Error`, we will reject registering hidden types already

Author: oli-obk

src/librustdoc/clean/blanket_impl.rs

@@ -47,7 +47,7 @@ impl<'a, 'tcx> BlanketImplFinder<'a, 'tcx> {
                 // Require the type the impl is implemented on to match
                 // our type, and ignore the impl if there was a mismatch.
                 let Ok(eq_result) = infcx.at(&traits::ObligationCause::dummy(), param_env).eq(
-                    DefineOpaqueTypes::No,
+                    DefineOpaqueTypes::Yes,
                     impl_trait_ref.self_ty(),
                     impl_ty,
                 ) else {