[iam] fix: use uuid4's first part for test (#3565)
[iam] fix: use uuid4's first part for test (#3565)

* [iam] fix: use uuid4's first part for test

fixes #3499

* fix test
GoogleCloudPlatform/python-docs-samples,GoogleCloudPlatform/python-docs-samples,GoogleCloudPlatform/python-docs-samples,GoogleCloudPlatform/python-docs-samples