[stringrefs] StringConst value should be non-nullable

Bug: v8:12868
Change-Id: Ia70ddb1fb25bc1f14259d14a8a9f614de7d8cd52
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3865558Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Manos Koukoutos <manoskouk@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82930}

src/wasm/constant-expression-interface.cc

@@ -151,7 +151,7 @@ void ConstantExpressionInterface::StringConst(
       isolate_->factory()
           ->NewStringFromUtf8(string_bytes, unibrow::Utf8Variant::kWtf8)
           .ToHandleChecked();
-  result->runtime_value = WasmValue(string, kWasmStringRef);
+  result->runtime_value = WasmValue(string, kWasmStringRef.AsNonNull());
 }
 
 namespace {