fix: skip test_client_helpers in non-grpc environments

Author: hebaalazzeh

packages/google-api-core/tests/unit/gapic/test_client_helpers.py

@@ -17,6 +17,11 @@
 from unittest import mock
 import pytest
 
+try:
+    import grpc  # noqa: F401
+except ImportError:
+    pytest.skip("No GRPC", allow_module_level=True)
+
 from google.api_core.gapic_v1 import client_helpers
 from google.auth.exceptions import MutualTLSChannelError