message: Fix -Wunused-but-set-variable.
  Cr-Commit-Position: refs/heads/main@{#35268}
diff: @@ -103,7 +103,7 @@ class LockRunner : public rtc::MessageHandlerAutoCleanup {
  locker_.Lock();
  shared_value = shared_value_;
  locker_.Unlock();
  - return shared_value_;
  + return shared_value;
  }
  void OnMessage(Message* msg) override {
  