Loosen an assertion to account for stashed errors.

The meaning of this assertion changed in #120828 when the meaning of
`has_errors` changed to exclude stashed errors. Evidently the new
meaning is too restrictive.

Fixes #120856.

compiler/rustc_hir_analysis/src/check/check.rs

@@ -1283,7 +1283,8 @@ fn check_type_alias_type_params_are_used<'tcx>(tcx: TyCtxt<'tcx>, def_id: LocalD
     let ty = tcx.type_of(def_id).instantiate_identity();
     if ty.references_error() {
         // If there is already another error, do not emit an error for not using a type parameter.
-        assert!(tcx.dcx().has_errors().is_some());
+        // Without the `stashed_err_count` part this can fail (#120856).
+        assert!(tcx.dcx().has_errors().is_some() || tcx.dcx().stashed_err_count() > 0);
         return;
     }