fix(assistant-v2): fix integration test for assistant v2

[nan2iz]

Thanks @kevinkowa for helping me fixing the issue on integration testing. I updated the PR based on our pair programming.

[kevinkowa]

we also need to delete the session, something like this is needed at the end of the test

object deleteSessionResponse = null;
            Log.Debug("AssistantV2IntegrationTests", "Attempting to DeleteSession...");
            service.WithHeader("X-Watson-Test", "1");
            service.DeleteSession(
                callback: (DetailedResponse<object> response, IBMError error) =>
                {
                    Log.Debug("AssistantV2IntegrationTests", "result: {0}", response.Response);
                    deleteSessionResponse = response.Result;
                    Assert.IsNotNull(response.Result);
                    Assert.IsNull(error);
                },
                assistantId: assistantId,
                sessionId: sessionId
            );

            while (deleteSessionResponse == null)
                yield return null;

[kevinkowa]

LGTM! Lets merge when the tests pass

[watson-github-bot]

🎉 This PR is included in version 5.2.0 🎉

The release is available on GitHub release

Your semantic-release bot 📦🚀