port: Fix test SendDirectLineMessage() (#6014)

[github-actions[bot]]

The changes in Fix test SendDirectLineMessage() (#6014) may need to be ported to maintain parity with microsoft/botbuilder-dotnet.

Fixes #minor

Description

This test has been failing intermittently in pipeline BotBuilder-DotNet-Functional-Tests-Linux-yaml. Apply the same fix as was done for https://github.com/microsoft/BotBuilder-Samples/blob/main/samples/csharp_dotnetcore/tests/Samples.EchoBot.FunctionalTests/DirectLineClientTests.cs

Please review and, if necessary, port the changes.