cppgc: Fix trace performance benchmark

Bug: v8:11635
Change-Id: I71c5542a503ca4b94fc3c8746e96fb0bc4e6c1f8
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2822628
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Omer Katz <omerkatz@chromium.org>
Auto-Submit: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Omer Katz <omerkatz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#73922}

test/benchmarks/cpp/cppgc/trace_perf.cc

@@ -40,7 +40,7 @@ class GCedWithMixin final : public GCed, public OtherPayload, public Mixin {
   }
 };
 
-class Holder : public cppgc::GarbageCollected<GCed> {
+class Holder : public cppgc::GarbageCollected<Holder> {
  public:
   explicit Holder(GCedWithMixin* object)
       : base_ref(object), mixin_ref(object) {}