Backport fixes for REST API version 6.0

The current dev branch as well recent releases focus on version 7.0 & 7.1 of the Azure DevOps REST API ,as mentioned in the documentation of the latter.

However, it would be interesting to backport fixes on top of older versions of the library addressing other REST API versions, matching other versions of the Azure DevOps (Server) product.

For instance, the current v6.0.0b4, the latest to support the 6.0 REST API version matchin Azure DevOps Server 2020.1, does not include fixex to the python package generating warning at the setuptools level when the package is being used.
Cf. this commit.

All fixes being meta or interesting for multiple versions of the REST API would be interesting to get for all the supported product.
Azure DevOps Server 2020, for instance, is supported until 2025 (and potentially 2030).
It is incoherent support for this library moves away from otherwise supported products.

检查 v6.0.0b4 package 和修复 setuptools 警告的引用 commit，然后将当前 dev branch 上的修复与受支持的 REST API 版本进行比较。确定哪些更改适用于 Azure DevOps Server 2020 和其他受支持的版本；完成标准是确定一致同意的 backport 范围以及相应的版本化 release。