message: Fix regression in UsrSctpReliabilityTest
  These tests, not run by default, were broken by
  Cr-Commit-Position: refs/heads/master@{#33738}
diff: @@ -250,7 +250,7 @@ class SctpDataSender final {
  rtc::Event sent_target_messages_count_{true, false};
  std::atomic<uint64_t> num_bytes_sent_ ATOMIC_VAR_INIT(0);
  absl::optional<std::string> last_error_;
  - webrtc::ScopedTaskSafety task_safety_;
  + webrtc::ScopedTaskSafetyDetached task_safety_;
  RTC_DISALLOW_COPY_AND_ASSIGN(SctpDataSender);
  };
  