[wasm] flag_liftoff_only should disable wasm-dynamic-tiering in cctest

FlagScope can't automatically disable wasm-dynamic-tiering.

Bug: v8:7748

Change-Id: Ieb59e20b4cb4436277aa88b615bca07657a1212c
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3578109
Auto-Submit: Yahan Lu <yahan@iscas.ac.cn>
Reviewed-by: Manos Koukoutos <manoskouk@chromium.org>
Commit-Queue: Manos Koukoutos <manoskouk@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79920}

test/cctest/wasm/test-gc.cc

@@ -40,6 +40,8 @@ class WasmGCTester {
                      execution_tier == TestExecutionTier::kLiftoff),
         flag_liftoff_only(&v8::internal::FLAG_liftoff_only,
                           execution_tier == TestExecutionTier::kLiftoff),
+        flag_wasm_dynamic_tiering(&v8::internal::FLAG_wasm_dynamic_tiering,
+                                  v8::internal::FLAG_liftoff_only != true),
         // Test both setups with canonicalization and without.
         flag_canonicalization(&v8::internal::FLAG_wasm_type_canonicalization,
                               execution_tier == TestExecutionTier::kTurbofan),
@@ -198,6 +200,7 @@ class WasmGCTester {
   const FlagScope<bool> flag_typedfuns;
   const FlagScope<bool> flag_liftoff;
   const FlagScope<bool> flag_liftoff_only;
+  const FlagScope<bool> flag_wasm_dynamic_tiering;
   const FlagScope<bool> flag_canonicalization;
   const FlagScope<bool> flag_tierup;