chore: update user creds for system test

[arithmetic1728]

No description provided.

[gnossen]

@arithmetic1728 I think this change may have broken the 2.4.0 release. google-auth does not declare a dependency on urllib3. grpcio is seeing this issue in CI:

  ...
  File "/var/local/git/grpc/src/python/grpcio_tests/tests/_loader.py", line 74, in walk_packages
    module = importer.find_module(module_name).load_module(module_name)
  File "<frozen importlib._bootstrap_external>", line 462, in _check_name_wrapper
  File "<frozen importlib._bootstrap_external>", line 962, in load_module
  File "<frozen importlib._bootstrap_external>", line 787, in load_module
  File "<frozen importlib._bootstrap>", line 265, in _load_module_shim
  File "<frozen importlib._bootstrap>", line 702, in _load
  File "<frozen importlib._bootstrap>", line 671, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 783, in exec_module
  File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed
  File "/var/local/git/grpc/src/python/grpcio_tests/tests_aio/interop/client.py", line 23, in <module>
    from tests.interop import client as interop_client_lib
  File "/var/local/git/grpc/src/python/grpcio_tests/tests/interop/client.py", line 24, in <module>
    from tests.interop import methods
  File "/var/local/git/grpc/src/python/grpcio_tests/tests/interop/methods.py", line 33, in <module>
    from google.auth.transport import requests as google_auth_transport_requests
  File "/var/local/git/grpc/py38/lib/python3.8/site-packages/google/auth/transport/requests.py", line 40, in <module>
    from urllib3.util.ssl_ import (
ModuleNotFoundError: No module named 'urllib3'