Fix memory leak of KeepAliveOperationTest.NotifiesObserversOnResponse

https://ci.chromium.org/p/chromium/builders/ci/Linux%20Chromium%20OS%20ASan%20LSan%20Tests%20%281%29/33985
deterministic failures
KeepAliveOperationTest.NotifiesObserversOnResponse
KeepAliveOperationTest.RecordsResponseDuration

https://logs.chromium.org/logs/chromium/buildbucket/cr-buildbucket.appspot.com/8910702062804733408/+/steps/chromeos_components_unittests/0/logs/Deterministic_failure:_KeepAliveOperationTest.NotifiesObserversOnResponse__status_FAILURE_ON_EXIT_/0

Change-Id: I034570a4376e8d39545c31dca035ff4f61c84510
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1660381Reviewed-by: Kyle Horimoto <khorimoto@chromium.org>
Commit-Queue: Takashi Sakamoto <tasak@google.com>
Cr-Commit-Position: refs/heads/master@{#712953}

chromeos/components/tether/keep_alive_operation_unittest.cc

@@ -43,7 +43,7 @@ class MockOperationObserver : public KeepAliveOperation::Observer {
 
   void OnOperationFinished(multidevice::RemoteDeviceRef remote_device,
                            std::unique_ptr<DeviceStatus> device_status) {
-    OnOperationFinishedRaw(remote_device, device_status.release());
+    OnOperationFinishedRaw(remote_device, device_status.get());
   }
 
  private: