list_pipelines() always throws AzureDevOpsAuthenticationError - azure-devops v7.1.0b4

Hi,

I can't get the list of Azure Pipelines because the function list_pipelines() always throws an AzureDevOpsAuthenticationError.

Steps to reproduce the error:

1. Create an Azure DevOps PAT with Full access.
2. Install the version 7.1.0b4: pip install azure-devops==7.1.0b4
3. Replace the parameter values with you PAT and Azure DevOps parameters and run this code:

from azure.devops.connection import Connection
from msrest.authentication import BasicAuthentication

personal_access_token = "PAT"
organization = "contoso"
project = "project-one"

credentials = BasicAuthentication('', personal_access_token)
connection = Connection(base_url=f'https://dev.azure.com/{organization}', creds=credentials)

pipelines_client = connection.clients.get_pipelines_client()
pipelines_list = pipelines_client.list_pipelines(project)

首先，使用提供的 Python 代码片段、azure-devops==7.1.0b4 和有效的 Azure DevOps PAT 重现该故障。跟踪 list_pipelines() 调用经过 pipelines 客户端和身份验证处理的过程；当该调用能够列出 pipelines 且不引发 AzureDevOpsAuthenticationError 时，即表示完成。