heap: Fix msvc compile due to unused return value

Bug: v8:12165
Change-Id: I54c7b429708a2d6a3c4db89911b9b69fa4a5a41a
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3250640
Auto-Submit: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Adam Klein <adamk@chromium.org>
Reviewed-by: Adam Klein <adamk@chromium.org>
Cr-Commit-Position: refs/heads/main@{#77600}

test/unittests/heap/traced-reference-unittest.cc

@@ -216,7 +216,9 @@ TEST_F(TracedReferenceTest, NoWriteBarrierOnConstruction) {
     SimulateIncrementalMarking();
     MarkCompactCollector::MarkingState state;
     ASSERT_TRUE(state.IsWhite(HeapObject::cast(*Utils::OpenHandle(*local))));
-    std::make_unique<v8::TracedReference<v8::Object>>(v8_isolate(), local);
+    auto ref =
+        std::make_unique<v8::TracedReference<v8::Object>>(v8_isolate(), local);
+    USE(ref);
     EXPECT_TRUE(state.IsWhite(HeapObject::cast(*Utils::OpenHandle(*local))));
   }
 }