{CI} Optimize the extension test: Use azdev test for testing, consistent with the main repo

[wangzelin007]

The old test uses python unittest, and the test log is as follows:

The new test uses azdev test, and the test log is as follows:

[yonzhan]

CI

[jiasli]

The intention of this metaclass is to add test methods to TestExtensionSource during the initialization of TestExtensionSource.

To verify that, we can add print(TestExtensionSource.__dict__.keys()) to L97 and check the output:

dict_keys(['__module__', 'setUp', 'tearDown', 'test_azext_account', 'test_azext_acrtransfer', 'test_azext_ad', 'test_azext_adp', 'test_azext_aem', 'test_azext_ai_examples', 'test_azext_aks_preview', 'test_azext_alertsmanagement', 

It generates a bunch of methods starting with test_ for each extension so that unittest can run them one by one.

Question is: what is the point of it, when it can simply be replaced by a for loop and invoke unittest or pytest on one extension in each iteration?