net - openai - tests pipeline has consistent test failures

[m-redding]

See pipeline history here: https://dev.azure.com/azure-sdk/internal/_build?definitionId=5839&_a=summary

This pipeline has been failing since May 30th.

Looking at recent runs, here are a sample of some of the failures:

Failed CanCreateAndModifyMessages(Azure) [89 ms]
Error Message:
System.ArgumentNullException : Value cannot be null. (Parameter 'uriString')

Failed CanCreateAndModifyMessages(NonAzure) [3 ms]
Error Message:
System.ArgumentNullException : Value cannot be null. (Parameter 'openAIApiKey')

Failed CanCreateRetrieveAndDeleteThreads(Azure) [1 ms]
Error Message:
System.ArgumentNullException : Value cannot be null. (Parameter 'uriString')

Failed CanCreateRetrieveAndDeleteThreads(NonAzure) [< 1 ms]
Error Message:
System.ArgumentNullException : Value cannot be null. (Parameter 'openAIApiKey')

Failed CanCreateRetrieveListAndDeleteAssistants(NonAzure) [6 ms]
Error Message:
System.ArgumentNullException : Value cannot be null. (Parameter 'openAIApiKey')

This was a blocker for me to be able to use this pipeline to validate changes in #46637