[wasm-gc] Drop values from liftoff for trivial ref.test

We need to drop the object and the rtt from the liftoff stack before
loading the result.

Bug: v8:7748
Change-Id: Idbd4878ededc35892c951cafb3f8a8298133adff
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3094015Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#76304}

src/wasm/function-body-decoder-impl.h

@@ -4426,6 +4426,8 @@ class WasmFullDecoder : public WasmDecoder<validate, decoding_mode> {
           if (V8_LIKELY(ObjectRelatedWithRtt(obj, rtt))) {
             CALL_INTERFACE(RefTest, obj, rtt, &value);
           } else {
+            CALL_INTERFACE(Drop);
+            CALL_INTERFACE(Drop);
             // Unrelated types. Will always fail.
             CALL_INTERFACE(I32Const, &value, 0);
           }